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Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station, May 2006
Volcano scheme.svg
Cross-section through a stratovolcano (vertical scale is exaggerated):
1. Large magma chamber
2. Bedrock
3. Conduit (pipe)
4. Base
5. Sill
6. Dike
7. Layers of ash emitted by the volcano
8. Flank
9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15. Ash cloud
Pinatubo ash plume reaching a height of 19 km, 3 days before the climactic eruption of 15 June 1991
A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, ash and gases to escape from below the surface. The word volcano is derived from the name of Vulcano island off Sicily which in turn, was named after Vulcan, the Roman god of fire.[1]
Volcanoes are generally found where tectonic plates are diverging or converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by convergent tectonic plates coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth's crust (called "non-hotspot intraplate volcanism"), such as in the African Rift Valley, the Wells Gray-Clearwater volcanic field and the Rio Grande Rift in North America and the European Rhine Graben with its Eifel volcanoes.
Volcanoes can be caused by mantle plumes. These so-called hotspots, for example at Hawaii, can occur far from plate boundaries. Hotspot volcanoes are also found elsewhere in the solar system, especially on rocky planets and moons.

Contents

Etymology

Kircher's model of the Earth's internal fires, from Mundus Subterraneus
The word volcano is thought to derive from Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn originates from Vulcan, the name of a god of fire in Roman mythology. The study of volcanoes is called volcanology, sometimes spelled vulcanology.

Plate tectonics and hotspots

Map showing the divergent plate boundaries (OSR – Oceanic Spreading Ridges) and recent sub aerial volcanoes.

Divergent plate boundaries

At the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust is being formed by hot molten rock slowly cooling and solidifying. The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates. The release of pressure due to the thinning of the crust leads to adiabatic expansion, and the partial melting of the mantle causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, therefore most volcanic activity is submarine, forming new seafloor. Black smokers or deep sea vents are an example of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, Iceland.
Indonesia - Lombok: Mount Rinjani - outbreak in 1994

Convergent plate boundaries

Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, creating magma. This magma tends to be very viscous due to its high silica content, so often does not reach the surface and cools at depth. When it does reach the surface, a volcano is formed. Typical examples for this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire.

Hotspots

Hotspots are not usually located on the ridges of tectonic plates, but above mantle plumes, where the convection of the Earth's mantle creates a column of hot material that rises until it reaches the crust, which tends to be thinner than in other areas of the Earth. The temperature of the plume causes the crust to melt and form pipes, which can vent magma. Because the tectonic plates move whereas the mantle plume remains in the same place, each volcano becomes dormant after a while and a new volcano is then formed as the plate shifts over the hotspot. The Hawaiian Islands are thought to be formed in such a manner, as well as the Snake River Plain, with the Yellowstone Caldera being the part of the North American plate currently above the hot spot.

Volcanic features

Conical Mount Fuji in Japan, at sunrise from Lake Kawaguchi (2005)
The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit. This describes just one of many types of volcano, and the features of volcanoes are much more complicated. The structure and behavior of volcanoes depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater, whereas others present landscape features such as massive plateaus. Vents that issue volcanic material (lava, which is what magma is called once it has escaped to the surface, and ash) and gases (mainly steam and magmatic gases) can be located anywhere on the landform. Many of these vents give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Hawaii's Kīlauea.
Lakagigar fissure vent in Iceland, source of the major world climate alteration of 1783-84.
Skjaldbreiður, a shield volcano whose name means "broad shield"
January 2009 image of the rhyolitic lava dome of Chaitén Volcano, southern Chile during its 2008-2009 eruption.
Holocene cinder cone volcano on State Highway 18 near Veyo, Utah.
Mayon, near perfect stratovolcano in the Philippines.
The Lake Toba volcano created a caldera 100 km long
Herðubreið, one of the tuyas in Iceland
Mud volcano on Taman Peninsular, Russia
Other types of volcano include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter, Saturn and Neptune; and mud volcanoes, which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes, except when a mud volcano is actually a vent of an igneous volcano.

Fissure vents

Volcanic fissure vents are flat, linear cracks through which lava emerges.

Shield volcanoes

Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent, but not generally explode catastrophically. Since low-viscosity magma is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland, as well.

Lava domes

Lava domes are built by slow eruptions of highly viscous lavas. They are sometimes formed within the crater of a previous volcanic eruption (as in Mount Saint Helens), but can also form independently, as in the case of Lassen Peak. Like stratovolcanoes, they can produce violent, explosive eruptions, but their lavas generally do not flow far from the originating vent.

Cryptodomes

Cryptodomes are formed when viscous lava forces its way up and causes a bulge. The 1980 eruption of Mount St. Helens was an example. Lava was under great pressure and forced a bulge in the mountain, which was unstable and slid down the North side.

Volcanic cones (cinder cones)

Volcanic cones or cinder cones are the result from eruptions that erupt mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 meters high. Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico, Caja del Rio is a volcanic field of over 60 cinder cones.

Stratovolcanoes (composite volcanoes)

Stratovolcanoes or composite volcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata that give rise to the name. Stratovolcanoes are also known as composite volcanoes, created from several structures during different kinds of eruptions. Strato/composite volcanoes are made of cinders, ash and lava. Cinders and ash pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the process begins again. Classic examples include Mt. Fuji in Japan, Mayon Volcano in the Philippines, and Mount Vesuvius and Stromboli in Italy. In recorded history, explosive eruptions by stratovolcanoes have posed the greatest hazard to civilizations.[citation needed]

Supervolcanoes

A supervolcano is a large volcano that usually has a large caldera and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulfur and ash erupted. They are the most dangerous type of volcano. Examples include Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico (both western United States), Lake Taupo in New Zealand, Lake Toba in Sumatra, Indonesia and Ngorogoro Crater in Tanzania. Supervolcanoes are hard to identify centuries later, given the enormous areas they cover. Large igneous provinces are also considered supervolcanoes because of the vast amount of basalt lava erupted, but are non-explosive.

Submarine volcanoes

Submarine volcanoes are common features on the ocean floor. Some are active and, in shallow water, disclose their presence by blasting steam and rocky debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them prevents the explosive release of steam and gases, although they can be detected by hydrophones and discoloration of water because of volcanic gases. Pumice rafts may also appear. Even large submarine eruptions may not disturb the ocean surface. Because of the rapid cooling effect of water as compared to air, and increased buoyancy, submarine volcanoes often form rather steep pillars over their volcanic vents as compared to above-surface volcanoes. They may become so large that they break the ocean surface as new islands. Pillow lava is a common eruptive product of submarine volcanoes. Hydrothermal vents are common near these volcanoes, and some support peculiar ecosystems based on dissolved minerals.

Subglacial volcanoes

Subglacial volcanoes develop underneath icecaps. They are made up of flat lava which flows at the top of extensive pillow lavas and palagonite. When the icecap melts, the lavas on the top collapse, leaving a flat-topped mountain. Then, the pillow lavas also collapse, giving an angle of 37.5 degrees[citation needed]. These volcanoes are also called table mountains, tuyas or (uncommonly) mobergs. Very good examples of this type of volcano can be seen in Iceland, however, there are also tuyas in British Columbia. The origin of the term comes from Tuya Butte, which is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analyzed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near the boundary with the Yukon Territory.

Mud volcanoes

Mud volcanoes or mud domes are formations created by geo-excreted liquids and gases, although there are several different processes which may cause such activity. The largest structures are 10 kilometers in diameter and reach 700 meters high.

Erupted material

Pāhoehoe Lava flow at Hawaii (island). The picture shows few overflows of a main lava channel.
The Stromboli volcano off the coast of Sicily has erupted continuously for thousands of years, giving rise to the term strombolian eruption ejecting lava bombs
. Mafic basalt flow created the Deccan Traps near Matheran, east of Mumbai, one of the largest volcanic features on earth.

Lava composition

Another way of classifying volcanoes is by the composition of material erupted (lava), since this affects the shape of the volcano. Lava can be broadly classified into 4 different compositions (Cas & Wright, 1987):
  • If the erupted magma contains a high percentage (>63%) of silica, the lava is called felsic.
    • Felsic lavas (dacites or rhyolites) tend to be highly viscous (not very fluid) and are erupted as domes or short, stubby flows. Viscous lavas tend to form stratovolcanoes or lava domes. Lassen Peak in California is an example of a volcano formed from felsic lava and is actually a large lava dome.
    • Because siliceous magmas are so viscous, they tend to trap volatiles (gases) that are present, which cause the magma to erupt catastrophically, eventually forming stratovolcanoes. Pyroclastic flows (ignimbrites) are highly hazardous products of such volcanoes, since they are composed of molten volcanic ash too heavy to go up into the atmosphere, so they hug the volcano's slopes and travel far from their vents during large eruptions. Temperatures as high as 1,200 °C are known to occur in pyroclastic flows, which will incinerate everything flammable in their path and thick layers of hot pyroclastic flow deposits can be laid down, often up to many meters thick. Alaska's Valley of Ten Thousand Smokes, formed by the eruption of Novarupta near Katmai in 1912, is an example of a thick pyroclastic flow or ignimbrite deposit. Volcanic ash that is light enough to be erupted high into the Earth's atmosphere may travel many kilometres before it falls back to ground as a tuff.
  • If the erupted magma contains 52–63% silica, the lava is of intermediate composition.
    • These "andesitic" volcanoes generally only occur above subduction zones (e.g. Mount Merapi in Indonesia).
    • Andesitic lava is typically formed at convergent boundary margins of tectonic plates, by several processes:
      • Hydration melting of peridotite and fractional crystallization
      • Melting of subducted slab containing sediments
      • Magma mixing between felsic rhyolitic and mafic basaltic magmas in an intermediate reservoir prior to emplacement or lava flow.
  • If the erupted magma contains <52% and >45% silica, the lava is called mafic (because it contains higher percentages of magnesium (Mg) and iron (Fe)) or basaltic. These lavas are usually much less viscous than rhyolitic lavas, depending on their eruption temperature; they also tend to be hotter than felsic lavas. Mafic lavas occur in a wide range of settings:
  • Some erupted magmas contain <=45% silica and produce ultramafic lava. Ultramafic flows, also known as komatiites, are very rare; indeed, very few have been erupted at the Earth's surface since the Proterozoic, when the planet's heat flow was higher. They are (or were) the hottest lavas, and probably more fluid than common mafic lavas.

Lava texture

Two types of lava are named according to the surface texture: ʻAʻa (pronounced [ˈʔaʔa]) and pāhoehoe ([paːˈho.eˈho.e]), both words having Hawaiian origins. ʻAʻa is characterized by a rough, clinkery surface and is the typical texture of viscous lava flows. However, even basaltic or mafic flows can be erupted as ʻaʻa flows, particularly if the eruption rate is high and the slope is steep.
Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Usually, only mafic flows will erupt as pāhoehoe, since they often erupt at higher temperatures or have the proper chemical make-up to allow them to flow with greater fluidity.

Volcanic activity

Damavand, highest volcano in Asia, is a potentially active volcano with fumaroles and solfatara near its summit.
Shiprock, the eroded remnant of the throat of an extinct volcano.
Map of volcanoes
Fourpeaked volcano, Alaska, in September 2007, after being thought extinct for over 10,000 years.

Scientific classification of volcanoes

Philippine Institute of Volcanology and Seismology provides a scientific classification system for volcanoes.[2]
Active - Eruption in historic times - Historical record - 500 years - C14 dating - 10,000 years - Local seismic activity - Oral / folkloric history
Potentially Active - Solfataras / Fumaroles - Geologically young (possibly erupted < 10,000 years and for calderas and large systems - possibly < 25,000 years). - Young-looking geomorphology (thin soil cover/sparse vegetation; low degree of erosion and dissection; young vent featuresl; +/- vegetation cover). - Suspected seismic activity. - Documented local ground deformation - Geochemical indicators of magmatic involvement. - Geophysical proof of magma bodies. - Strong connection with subduction zones and external tectonic settings.
Inactive No record of eruption and its form is beginning to change by the agents of weathering and erosion via formation of deep and long gullies.

Popular classification of volcanoes

Active

A popular way of classifying magmatic volcanoes is by their frequency of eruption, with those that erupt regularly called active, those that have erupted in historical times but are now quiet called dormant, and those that have not erupted in historical times called extinct. However, these popular classifications—extinct in particular—are practically meaningless to scientists. They use classifications which refer to a particular volcano's formative and eruptive processes and resulting shapes, which was explained above.
There is no real consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By human lifespans, however, they are not.
Scientists usually consider a volcano to be erupting or likely to erupt if it is currently erupting, or showing signs of unrest such as unusual earthquake activity or significant new gas emissions. Most scientists consider a volcano active if it has erupted in holocene times. Historic times is another timeframe for active. But it is important to note that the span of recorded history differs from region to region. In China and the Mediterranean, recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States and Canada, it reaches back less than 300 years, and in Hawaii and New Zealand, only around 200 years. The Smithsonian Global Volcanism Program's definition of active is having erupted within the last 10,000 years (the 'holocene' period).

Extinct

Extinct volcanoes are those that scientists consider unlikely to erupt again, because the volcano no longer has a lava supply. Examples of extinct volcanoes are many volcanoes on the Hawaiian Islands in the U.S. (extinct because the Hawaii hotspot is centered near the Big Island), and Paricutin, which is monogenetic. Otherwise, whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" calderas can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct. For example, the Yellowstone Caldera in Yellowstone National Park is at least 2 million years old and hasn't erupted violently for approximately 640,000 years, although there has been some minor activity relatively recently, with hydrothermal eruptions less than 10,000 years ago and lava flows about 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e. the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be an active volcano.

Dormant

It is difficult to distinguish an extinct volcano from a dormant one. Volcanoes are often considered to be extinct if there are no written records of its activity. Nevertheless volcanoes may remain dormant for a long period of time, and it is not uncommon for a so-called "extinct" volcano to erupt again. Vesuvius was thought to be extinct before its famous eruption of AD 79, which destroyed the towns of Herculaneum and Pompeii. More recently, the long-dormant Soufrière Hills volcano on the island of Montserrat was thought to be extinct before activity resumed in 1995. Another recent example is Fourpeaked Mountain in Alaska, which, prior to its eruption in September 2006, had not erupted since before 8000 BC and was long thought to be extinct.

Notable volcanoes

Koryaksky volcano towering over Avacha Bay on Kamchatka Peninsula, Far Eastern Russia.
The 16 current Decade Volcanoes are:

Effects of volcanoes

Volcanic "injection"
Solar radiation reduction from volcanic eruptions
Sulfur dioxide emissions by volcanoes.
Average concentration of sulfur dioxide over the Sierra Negra Volcano (Galapagos Islands) from October 23–November 1, 2005
There are many different types of volcanic eruptions and associated activity: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.
The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.
Large, explosive volcanic eruptions inject water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 16–32 kilometres (10–20 mi) above the Earth's surface. The most significant impacts from these injections come from the conversion of sulfur dioxide to sulfuric acid (H2SO4), which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the Earth's albedo—its reflection of radiation from the Sun back into space - and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years — sulfur dioxide from the eruption of Huaynaputina probably caused the Russian famine of 1601 - 1603. The sulfate aerosols also promote complex chemical reactions on their surfaces that alter chlorine and nitrogen chemical species in the stratosphere. This effect, together with increased stratospheric chlorine levels from chlorofluorocarbon pollution, generates chlorine monoxide (ClO), which destroys ozone (O3). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for cirrus clouds and further modify the Earth's radiation balance. Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon for biogeochemical cycles.
Rainbow and volcanic ash with sulfur dioxide emissions from Halema`uma`u vent.
Gas emissions from volcanoes are a natural contributor to acid rain. Volcanic activity releases about 130 to 230 teragrams (145 million to 255 million short tons) of carbon dioxide each year.[3] Volcanic eruptions may inject aerosols into the Earth's atmosphere. Large injections may cause visual effects such as unusually colorful sunsets and affect global climate mainly by cooling it. Volcanic eruptions also provide the benefit of adding nutrients to soil through the weathering process of volcanic rocks. These fertile soils assist the growth of plants and various crops. Volcanic eruptions can also create new islands, as the magma cools and solidifies upon contact with the water.

Volcanoes on other planetary bodies

Olympus Mons (Latin, "Mount Olympus") is the tallest known mountain in our solar system, located on the planet Mars.
The Earth's Moon has no large volcanoes and no current volcanic activity, although recent evidence suggests it may still possess a partially molten core.[4] However, the Moon does have many volcanic features such as maria (the darker patches seen on the moon), rilles and domes.
The planet Venus has a surface that is 90% basalt, indicating that volcanism played a major role in shaping its surface. The planet may have had a major global resurfacing event about 500 million years ago,[5] from what scientists can tell from the density of impact craters on the surface. Lava flows are widespread and forms of volcanism not present on Earth occur as well. Changes in the planet's atmosphere and observations of lightning, have been attributed to ongoing volcanic eruptions, although there is no confirmation of whether or not Venus is still volcanically active. However, radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus's highest volcano Maat Mons, in the form of ash flows near the summit and on the northern flank.
There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth. They include Arsia Mons, Ascraeus Mons, Hecates Tholus, Olympus Mons, and Pavonis Mons. These volcanoes have been extinct for many millions of years,[6] but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well.[6]
The Tvashtar volcano erupts a plume 330 km (205 mi) above the surface of Jupiter's moon Io.
Jupiter's moon Io is the most volcanically active object in the solar system because of tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur, sulfur dioxide and silicate rock, and as a result, Io is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1,800 K (1,500 °C). In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io.[7] Europa, the smallest of Jupiter's Galilean moons, also appears to have an active volcanic system, except that its volcanic activity is entirely in the form of water, which freezes into ice on the frigid surface. This process is known as cryovolcanism, and is apparently most common on the moons of the outer planets of the solar system.
In 1989 the Voyager 2 spacecraft observed cryovolcanoes (ice volcanoes) on Triton, a moon of Neptune, and in 2005 the Cassini-Huygens probe photographed fountains of frozen particles erupting from Enceladus, a moon of Saturn.[8] The ejecta may be composed of water, liquid nitrogen, dust, or methane compounds. Cassini-Huygens also found evidence of a methane-spewing cryovolcano on the Saturnian moon Titan, which is believed to be a significant source of the methane found in its atmosphere.[9] It is theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar.
A 2010 study of the exoplanet COROT-7b, which was detected by transit in 2009, studied that tidal heating from the host star very close to the planet and neighboring planets could generate intense volcanic activity similar to Io.[10]

In culture

Past beliefs

Many ancient accounts ascribe volcanic eruptions to supernatural causes, such as the actions of gods or demigods. To the ancient Greeks, volcanoes' capricious power could only be explained as acts of the gods, while 16th/17th-century German astronomer Johannes Kepler believed they were ducts for the Earth's tears. [11] One early idea counter to this was proposed by Jesuit Athanasius Kircher (1602–1680), who witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal.
Various explanations were proposed for volcano behavior before the modern understanding of the Earth's mantle structure as a semisolid material was developed. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to chemical reactions and a thin layer of molten rock near the surface.

Panoramas

Black Rock Volcano an extinct cinder cone near Fillmore, Utah.
Vulcano island with the north coast of Sicily in the background.
Remote Binubulauan in Kalinga province, central northern Luzon, Philippines, April 2009

See also

Lists
Specific locations
People

Further reading

  • Marti, Joan and Ernst, Gerald. (2005). Volcanoes and the Environment. Cambridge University Press. ISBN 0-521-59254-2. 
  • Macdonald, Gordon A., and Agatin T. Abbott. (1970). Volcanoes in the Sea. University of Hawaii Press, Honolulu. 441 p.
  • Ollier, Cliff. (1988). Volcanoes. Basil Blackwell, Oxford, UK, ISBN 0-631-15664-X (hardback), ISBN 0-631-15977-0 (paperback).
  • Haraldur Sigurðsson, ed. (1999) Encyclopedia of Volcanoes. Academic Press. ISBN 0-12-643140-X. This is a reference aimed at geologists, but many articles are accessible to non-professionals.
  • Cas, R.A.F. and J.V. Wright, 1987. Volcanic Successions. Unwin Hyman Inc. 528p. ISBN 0-04-552022-4

References

  1. ^ Douglas Harper (November 2001). "Volcano". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=volcano. Retrieved 2009-06-11. 
  2. ^ [1]
  3. ^ "Volcanic Gases and Their Effects" (HTML). U.S. Geological Survey. http://volcanoes.usgs.gov/Hazards/What/VolGas/volgas.html. Retrieved 2007-06-16. 
  4. ^ M. A. Wieczorek, B. L. Jolliff, A. Khan, M. E. Pritchard, B. P. Weiss, J. G. Williams, L. L. Hood, K. Righter, C. R. Neal, C. K. Shearer, I. S. McCallum, S. Tompkins, B. R. Hawke, C. Peterson, J, J. Gillis, B. Bussey (2006). "The Constitution and Structure of the Lunar Interior". Reviews in Mineralogy and Geochemistry 60 (1): 221–364. doi:10.2138/rmg.2006.60.3. 
  5. ^ D.L. Bindschadler (1995). "Magellan: A new view of Venus' geology and geophysics". American Geophysical Union. http://www.agu.org/journals/rg/rg9504S/95RG00281/index.html. Retrieved 2006-09-04. 
  6. ^ a b "Glacial, volcanic and fluvial activity on Mars: latest images". European Space Agency. 2005-02-25. http://www.esa.int/esaMI/Mars_Express/SEMLF6D3M5E_0.html. Retrieved 2006-08-17. 
  7. ^ Exceptionally Bright Eruption on lo Rivals Largest in Solar System, Nov. 13, 2002
  8. ^ PPARC, Cassini Finds an Atmosphere on Saturn's Moon Enceladus
  9. ^ NewScientist, Hydrocarbon volcano discovered on Titan, June 8, 2005
  10. ^ Jaggard, Victoria (2010-02-05). ""Super Earth" May Really Be New Planet Type: Super-Io". National Geographic web site daily news. National Geographic Society. http://news.nationalgeographic.com/news/2010/02/100205-new-type-planet-corot-7b-io/. Retrieved 2010-03-11. 
  11. ^ Micheal Williams (11-2007). "Hearts of fire". Morning Calm (Korean Air Lines Co., Ltd.) (11-2007): 6. 

External links



Quotes

Up to date as of January 14, 2010
(Redirected to Volcano (film) article)

From Wikiquote

.Volcano is a 1997 disaster-action movie starring Tommy Lee Jones about a volcano growing out of the La Brea Tar Pits and wreaking havoc throughout Los Angeles.^ For instance, as when Jaye didnt see the ash tower, a post-production effect of a huge tower of lava is shown fountaining up from the La Brea Tar Pits.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ "In this lesson, students explore first-person accounts of volcanic eruptions throughout time and use the Internet to access second-hand information about volcanoes.
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

^ Heche, meanwhile, having in fact identified the material as "la-va," or something, tells Jones he must evacuate the West Side of Los Angeles.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

Written by Jerome Armstrong and Billy Ray and directed by Mick Jackson.
The Coast is Toast. Taglines

Contents

Mike Roark

.
  • I enjoy motor sports, music and the company of close friends…sir.
  • [Responding to a phone call on his private line] Oh, that'll be my little girl wanting a tattoo.
  • We're going to put as many people in front of it as it takes.^ "Now, when we want to be able to go home, the worst thing we can do is to take the wrong decisions," she said.

    ^ Despite the danger, many people have stayed put over the last month, citing the need to guard their homes and look after crops and animals.

    Listen up, people! .Let me tell you what's south of us: no more museums, no more department stores, just homes!^ Tell us now, what was the weather like when you followed Clue #8, and what is it like when you follow this button and see your closest camera view for Clue #9 ?
    • Webchat 23 September 2009 4:43 UTC www.rain.org [Source type: General]

    People! If we turn and run now, they're going to be defenseless! You don't like my plan? That's good. Give me another plan, but don't tell me we're backing out!

Amy Barnes

.
  • [after arriving at the Tar Pits] You would have loved this, Rachel.
  • It's a lava bomb.^ For instance, as when Jaye didnt see the ash tower, a post-production effect of a huge tower of lava is shown fountaining up from the La Brea Tar Pits.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ Again here, if you at all pay attention to where we last saw the lava and how quickly it was moving, it would have engulfed the characters as Jones explained his plan.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    You don't do anything...until you know where it's gonna land.
  • When Mount St. Helens blew the force was 27,000 times greater than that of the Hiroshima bomb.

Emmit Reese

  • Bob, we need pictures. .I need those choppers in the air now.
  • Sounded like you said "something like a meteor"?
  • I just got a little message here from Sindelar.^ This again illustrates why you need somebody with a good gut feeling, because otherwise you keep demanding scientific proof and evidence that somethings going on.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ Just so we know that the Evil Public Works Chief was wrong when he said that steam caused the accident (duh), Jaye notes that "Steam doesnt char clothing like this!"
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ You didnt think wed get out of here without being force fed an Important Environmental Message, did you?
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    He's stuck on the damn freeway directing traffic.

Others

  • Roger Lapher: Freak accident on a storm drain job. They hit a steam pocket and got scalded. No fires, no explosions, no continuing threat. We'll copy you on a report.
  • Roger: You're not happy unless you’re declaring an emergency, are you!
  • Anita: Yeah, well, I'm doing him a favor, a big favor. I'm gonna miss my class. [phone rings and Anita picks it up] Hello? Mike! Oh, fine; a perfect little ray of sunshine like I was after my parents separated. .Every couple of minutes her head comes off her shoulders, rotates 360 degrees, and then she starts watching TV again.
  • Chief Sindelar: Gonna be delayed.^ Additionally, students will need a small amount of class time (approximately 5 minutes) every day for a couple of weeks to record current earthquakes."
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    .My damn car's stuck behind the damn gate cos we have no damn power!
  • Bud McVie: Hey, man, you know what they say.^ Perhaps you want to know whether earthquakes or volcanoes are more powerful or destructive.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    ^ And, exactly as in that film, they must have eventually realized that he served no real purpose, and cut his part down to the point where you wonder why he was even in the film.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ Also, you will have to let the islanders know what the consequences are in case they decide not to leave.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    No pain, no gain.

Dialogue

.
  • Mike: I can't leave you here after an earthquake.
  • Kelly Roark: Why not?^ "Have you wondered why this WebQuest is called "Spaghetti Earthquake"?
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    ^ Maybe you need to determine why earthquakes and volcanoes occur.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    ^ It would be most beneficial for you to find out why and where earthquakes happen and how they are measured.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    I'm 13 years old. .I know what to do.
  • Mike: OK. What do you do?
  • Kelly: Get in the door frame, stick your head between your knees, and kiss your ass goodbye.

  • Bud McVie: Oh-oh, we're cool now.^ OK, if you havent thrown up from the films saccharine racial message prior to this, you better get your vomit bag out.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ Did you know that its OK to be driving directly in front of a crashing helicopter?
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    It's LAPD.
  • Scared Man: Hey, officer! .How about giving us a ride back to civilization please?
  • Bud McVie: What's up?^ (How about sending the cops up there to evacuate the old bag by force?
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ One of the involved drivers is white, and, of course, a racist, asking the officers to "drive us back to civilization."
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    You gonna come out or what? .It's our 'hood!
  • Terry Jasper: Hey, you wanna calm down and tell me what this is all about?
  • Bud McVie: You wanna get outta my face?
  • Terry Jasper: Hey, if I'm in your face, you’re gonna know it, all right; bro?
  • Bud McVie: Huh, right!

  • Rachel: I can't.^ You know, the rival movies about runner Steve Prefontaine?
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ It is your job to find out as much as you can about these two natural disasters and submit a report to the mayor of the town about your findings.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    ^ Somehow the congregated extras all seem to hear his wee voice and look at each other with eyes opened for the first time and realize, hey, the kids right.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    .I can't.
  • Kevin: It's only couple of sentences, maybe a question or two.
  • Rachel: Then you do it!
  • Kevin: When the ground moves, people wanna hear from a seismologist, not a pencil pusher.
  • Rachel: If I go up there, I am gonna throw up.
  • Kevin: I don’t think that’s gonna send the sense of calm we're looking for.
  • Amy: Hey, you guys didn't feel anything this morning, did you?
  • Kevin: You're off the hook, Flash.
  • Amy: Oh, you weren't gonna make her talk to those nasty reporters, were you?
  • Rachel: I got some stuff I wanna show you later.
  • Amy: Okay.

  • Mike: If a dam breaks somewhere, the Mayor calls, I don't want you telling her Roark went fishing.
  • Emmit: Look, see, the mayor's in Aspen, okay?^ "What do you think the odds are against an eruption up there?
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ Nicotine Patch Guy shows up (told you!
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ There will be other questions that you will need to answer along the way."
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    We don't pull her off of the slopes for only a 4.9. Besides, I'd cover for you.
  • Mike: I'm sure you would. .You look very comfortable sitting behind my desk talking on my telephone.
  • Emmit: Yeah, it's kinda like I belong there or something.

  • Traffic Cop: I don't care what your supervisor said!^ Bring something to quench your thirst after the climb; there's no drinking water at the park.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    ^ "If it is necessary, send my wife and girls to the shelter, but I am staying to look after my animals," said Manuel Cuellar, a local coffee grower.

    ^ Its like that board game where you try to depict something without using the provided list of descriptive words.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    Nobody ran a work order past me, and this vehicle is on public property!
  • DWP Worker 1: What are you gonna do, ticket us?
  • Traffic Cop:Oh,You're the cute one. .How 'bout I tow your ass, honey?

  • Roger: You're not happy unless you’re declaring an emergency, are you!
  • Mike: No, actually I enjoy motor sports, music and the company of close friends…sir.
  • Stan Olber: 30,000 people think they're taking the train home tonight.^ People, have you no shame?
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ And, exactly as in that film, they must have eventually realized that he served no real purpose, and cut his part down to the point where you wonder why he was even in the film.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ Up to 20,000 people live in the danger zone, taking advantage of the rich volcanic soil.

    What am I supposed to do for them?
  • Mike: Put on extra buses.
  • Stan: It's his mess. Let him take the shit for it.

  • Chief Sindelar: Tell him he's not in Kansas anymore.
  • Emmit: You're not in Kansas anymore Mike.
  • Mike: St. Louis, I'm not in St. Louis.
  • Emmit: [into phone] St. Louis, he's not in St. Louis.
  • Sindelar: I don't give a shit where's he's not! .He has a desk now; that's where...
  • Emmit: [to Mike] You have a desk; that's where you work.

  • Amy: Sometimes magma can find one of those fissures and rise up through it.
  • Mike: What's magma?
  • Rachel: Lava.
  • Mike: Lava?^ You will also find out information about how to live through an earthquake and the safety procedures that should be taken."
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    ^ This proves the calm before the storm in more ways than one, however, as the actual eruption of a gigantic creeping flow of lava now begins.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ As we look down the long, straight street that for blocks back is full of bright, glowing lava, a reporter suddenly announces, "Now you can see it."
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    .Right here in L.A?
  • Amy: It is one of the possibilities.
  • Mike: We have a history of that here in the downtown area?
  • Rachel: Parícutin...1943 a Mexican farmer sees smoke coming out of the middle of his cornfield.^ Here we see Heche finally making it out of the tunnel, allowing her a short and not-terribly-affecting "Oh, woe, my friend is dead!"
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ As compared to the eruption of 1956, the only one in the history of modern observations, the current eruption started in a more impetuous and powerful way the scientist pointed out.

    ^ Looking out from their soon-to-be penthouse apartment, Norman says "Heres how I see our future."
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    A week later there's a volcano a thousand feet high. There's no history of anything until it happens. Then there is.

[Guards are moving paintings from the L.A. County Art Museum]
  • 1st Guard: Man, this Hieronymus Bosch is heavy!
  • 2nd Guard: That's because he deals with man's inclination towards sin, in defiance of God's will.
  • 1st Guard: I didn't mean it like that.
  • 2nd Guard: Oh.

[Mike ordered 200 K-rails (freeway dividers) to redirect the lava.]
  • Mike: Where's the rest of 'em?
  • Truck driver: What "rest of 'em?" This is it!
  • Lt. Fox: Hey, there only about eighty here!
  • Truck driver: Eighty-two; everything else is stuck on the 5 and the 10.
  • Lt. Fox: We're trying to keep the city in one piece, pinhead. Eighty rails ain't gonna do it!
  • Truck driver: So what are you blaming me for?
  • Lt. Fox: Convenience, ok?

  • Roger: Didn't you hear me? I said the lights are out in San Francisco.
  • L.A. Fire Chief: But this street's on fire. Nobody gives a shit about San Francisco!

  • Woman: Emmit, FAA’s on the line. They want an update.
  • Emmit: Where are we with the airports?
  • Marty: We shut down all outgoing. Everything incoming is being re-routed to Ontario.
  • Emmit: No, no, no, no. Marty, no…Look at that screen! That cloud is blowing due east. We gotta send everything to San Diego.
  • Man: Emmit, they got two gas lines burning on Fairfax. They can't get any hydrant pressure.
  • Emmit: Swimming pools.
  • Man: What about them?
  • Emmit: Pump out all the swimming pools. That's a thousand gallons a pop. That's all the water we need.
  • Man: Emmit, we just got a call from La Brea. .There's total gridlock from Pico to Sunset.
  • Emmit: Didn't we send over all those damn traffic cops?
  • Man: That's who's calling; they're stuck at Olympic.^ Hmm, funny how with all those people desperately searching the rubble for sign of Jones and the kids, that it should be Heche who spots them first.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ Meanwhile, racial tensions are immediately manifested between a Proud Black Man Whos Not Going to Take it Any More and a Racist White Cop.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ I am calling on all amateur space weather monitors to send in your independent reports.

    .Cars keep stalling out because of all the ash.^ On St. Croix, a man died when his car swerved off the road because of poor visibility due to the ash, U.S. Virgin Islands police said.

    .It's clogging up the air filters.
  • Emmit: Chevettes, right?

  • Amy: [calling Roark on his phone] How fast can you get to the corner of Wilshire and Western, we got a problem.
  • Mike: No, no.^ "This lesson is designed to help you understand what volcanoes are, their make-up, and how they are classified.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    Not anymore. .We have it stopped.
  • Amy: The volume of ash coming down is way too high to think that we're out of danger.
  • Mike: So, why did it just stop?
  • Amy: Well, maybe it didn't, maybe it just went someplace else.
  • Mike: So, how do you know it didn't stop?
  • Amy: You know, I don't.^ You will discover why and how these numbers are related."
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    ^ Did you know that its OK to be driving directly in front of a crashing helicopter?
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ Well, guess what, we did, and it just makes our Heroine look like a moron to have her explain this exotic property of acid.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    .But when Mount Saint Helens blew, the force was twenty seven thousand times greater then that of the Hiroshima bomb.^ Mount Sakurajima, which is located southwest of Tokyo, belched out lava at least seven times after it initially blew.

    ^ The eruptions were 42 times greater than those of Mount St. Helens in 1980.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    ^ In order to make him listen, she notes that the Mount St. Helens eruption generated forces 27,000 times that of the Hiroshima atomic bomb.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    .Do you think that vent released anywhere near that much energy yet?
  • Mike: No.
  • Amy: Well, lets just assume that we haven't seen the real bulk of the magma yet, okay?^ Derrick Cave Lava Tube: 19 Near the main vent, much of the lava flowed through a narrow, open gutter and formed a large, sinuous, well-developed lava tube, Derrick Cave.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    ^ You might think that Im making much ado out of nothing here.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    ^ The idea that you would drive anywhere near this thing is noticeably insane.
    • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

    Trust me, get down here. [hangs up the phone] Shit.

  • Kelly: Rock beats scissor and scissor beats paper.
  • Tommy: I'm not paper; I'm lava. What beats that?
  • Kelly: My dad...I hope!

[last lines]
  • Text on screen: C.I.G.S. Volcano Databank
  • Text on screen: Name: Mount Wilshire
  • Text on screen: Location: Los Angeles, California
  • Text on screen: Status: ACTIVE

Taglines

.
  • The Coast Is Toast.
  • There are at least 1,500 active volcanoes that we know about...and at least one that we don't.
  • Welcome to Los Angeles.^ It is also one of the most active volcanoes in the Aleutians.

    ^ Lava has oozed from a new location on Kilauea, one of the worlds most active volcanoes, scientists said.

    ^ Then you will list information in a table on at least five active volcanoes from the ring of fire.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    It's hotter than hell.

External Links

Wikipedia
Wikipedia has an article about:

Travel guide

Up to date as of January 14, 2010
(Redirected to Volcanoes article)

From Wikitravel

This article is a travel topic.
.Volcanoes come in all sorts of shapes and sizes.^ These different types of volcanoes come in different shapes and erupt in various ways.
  • Volcanoes | Universe Today 3 February 2010 19:019 UTC www.universetoday.com [Source type: FILTERED WITH BAYES]

.Although the name evokes images of the conical mountain spewing ash and lava, such events are rare though often newsworthy, and are probably best seen on the TV news rather than witnessed up close and in person.^ The recent flows on the pali show up much lighter in color than the older lava beneath.
  • Kilauea Volcano Eruption Update & Information 3 February 2010 19:019 UTC www.volcanogallery.com [Source type: FILTERED WITH BAYES]

^ For instance, as when Jaye didnt see the ash tower, a post-production effect of a huge tower of lava is shown fountaining up from the La Brea Tar Pits.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ DI events often correlate with lava pulses and/or pauses in the eruption at the Pu`u `O`o/July 21/TEB vents.
  • Kilauea Volcano Eruption Update & Information 3 February 2010 19:019 UTC www.volcanogallery.com [Source type: FILTERED WITH BAYES]

.However, many volcanoes around the world are tourist attractions in their own right and are worth a visit, so one can appreciate the awesome power of nature in person.^ A few other Squidoo Members have visited volcanoes and shared their own photos and memories!
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Here's some links to other web pages sharing volcano myths -- "geomythology" -- from around the world.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ A s of the 1st of January, Mount Etna is one of the most active volcanoes in the world and is in an almost constant state of activity.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

Mts. Bromo and Semeru in action, Java, Indonesia
Mts. Bromo and Semeru in action, Java, Indonesia

Understand

.Some of the largest volcanoes on earth are not recognisable as such.^ Chile's chain of some 2,000 volcanoes is the world's second-largest after Indonesia's.

^ These are some of the most active -- and peaceful -- volcanoes on Earth.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

.For example, Yellowstone in the United States, Toba in Indonesia, and Taupo in New Zealand are known as super-volcanoes.^ New Zealand Volcano Cams This page has links to cams for several of New Zealand's volcanoes, plus current seismograph readings.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ They are now known as Novy Tolbachik or New Tolbachik volcano.
  • Kamchatkan volcanoes 3 February 2010 19:019 UTC maurice.strahlen.org [Source type: FILTERED WITH BAYES]

^ Latest news of supervolcano YELLOWSTONE CALDERA in Wyoming in the United States in the "Restless Volcanoes Status Report" section.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

.They are generally in the form of large calderas, which are giant volcanic depressions formed either by large explosive eruptions or quiet long-term drainage of magma, and they often have associated lava flows or domes.^ Derrick Cave Lava Tube: 19 Near the main vent, much of the lava flowed through a narrow, open gutter and formed a large, sinuous, well-developed lava tube, Derrick Cave.
  • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

^ A pyroclastic-surge and pumice layer that was considered to originate from the eruption that formed the elliptical 2.5 x 4 km wide summit caldera was dated at about 9400 years ago.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

^ Overlapping shield volcanoes that formed around major vents extruded a complex of basaltic lava flows in some places.
  • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

.Most supervolcanoes are explosive in origin and have undergone unimaginably huge eruptions in the geologic past.^ Tungurahua has had at least seventeen eruptions in historical times, its most recent occurring in 1944 when it erupted explosively from its central crater.

^ Includes eruption summaries, reports, data and references to most volcanoes that have been active over the past 11,000 years.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, which is located immediately south of Karymsky volcano.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

.However, it is important to note that such volcanoes have erupted violently very infrequently, usually only once every 100,000-800,000 years.^ Volcano erupts after 9000 years .
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Chile's Chaiten Volcano, which erupted spectacularly last year, spewed a vast cloud of ash on Thursday in what appeared to be a partial collapse of its cone.

^ The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months.

Hence, there is no reason to worry that Yellowstone, for example, will explode within your lifetime! .Many are so big that, for many years, geologists did not appreciate that these features were volcanoes in their own rights.^ Stromboli Online This multi-lingual website actually covers many more volcanoes than Stromboli, and features some spectacular photography.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ By construction and examining the model, students will obtain a greater appreciation of the relationship between the internal structure of the volcano and its exterior shape and features.
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

^ Many structural features in these flows are similar to structural features in flows that compose most of the Pliocene and younger basaltic-rock aquifers.
  • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

.Compared to these, the currently active volcanoes on earth are relatively quite small!^ These are some of the most active -- and peaceful -- volcanoes on Earth.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ They then synthesize their knowledge by creating and presenting reports about currently active volcanoes around the world."
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

^ EARTHS ACTIVE VOLCANOES http://www.geo.mtu.edu/volcanoes/world.html Lists Earths active volcanoes by geographical region.
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

.Although there are literally hundreds of active volcanoes around the world, there are many more that are extinct.^ Imagine being in an active volcano, and standing literally three feet away from the main pool of lava.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ Lava has oozed from a new location on Kilauea, one of the worlds most active volcanoes, scientists said.

^ Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

.One can still appreciate the awesome power of nature from such places without the hazards that go with active volcanoes.^ It is also one of the most active volcanoes in the Aleutians.

^ The volcano still poses a hazard to the local population with ashfall and acid rain affecting food crops and drinking water.

^ T he eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

.A volcano is defined as active if it has erupted within the last 10,000 years (less than a second in geological time!^ Volcano erupts after 9000 years .
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Io, Jupiter's Volcanic Moon This moon of Jupiter caught everyone by surprise when the space probe Voyager passed by: it had active, erupting volcanoes!
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Much of its > 530,000 year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

), according to the .Smithsonian Global Volcanism Program, the major volcano monitoring organization based in Washington, DC. One that is active but not currently erupting is considered dormant.^ It is also one of the most active volcanoes in the Aleutians.

^ Io, Jupiter's Volcanic Moon This moon of Jupiter caught everyone by surprise when the space probe Voyager passed by: it had active, erupting volcanoes!
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ N evado del Huila, the highest active volcano in Colombia, is an elongated N-S-trending volcanic chain mantled by a glacier icecap.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

.Any volcano that has not erupted for more than 10,000 years and often, but not always, lacking geothermal heat and activity, may be considered extinct.^ Mount Jefferson last erupted more than 20,000 years ago.
  • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

^ Volcano erupts after 9000 years .
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Some extinct volcanoes are nothing more than a small mountain, similar in appearance to the surrounding mountains.
  • Kamchatkan volcanoes 3 February 2010 19:019 UTC maurice.strahlen.org [Source type: FILTERED WITH BAYES]

.(But this is problematic when dealing with supervolcanoes because of their long and slow cycles of activity, and not to mention that some supposedly extinct volcanoes can come back to life).^ Some extinct volcanoes are nothing more than a small mountain, similar in appearance to the surrounding mountains.
  • Kamchatkan volcanoes 3 February 2010 19:019 UTC maurice.strahlen.org [Source type: FILTERED WITH BAYES]

^ After this activity the volcano went back to steady levels.

^ Because often several volcanoes can be found in a single complex I put some together under a single entry.
  • Kamchatkan volcanoes 3 February 2010 19:019 UTC maurice.strahlen.org [Source type: FILTERED WITH BAYES]

Geothermal Areas

.Throughout volcanic areas of the world, one may also encounter geothermal areas.^ It is popular with mountaineers and is seen as having one of the world's most perfect volcanic cone shapes.

These places are often, but not always, associated with volcanic activity. .Hot springs, geysers, mud pools and fumaroles (steam/gas vents) are common features in geothermal areas, and can be scenic and hot springs can be great places to take a dip in.^ The temperature of the fumarols vary from 50 to 900C. Apart from the common fumarolic gasses elements measured in the gas include Cu, Pb, Mo, Zn, Bi and Ag.
  • Kamchatkan volcanoes 3 February 2010 19:019 UTC maurice.strahlen.org [Source type: FILTERED WITH BAYES]

^ Yellowstone Volcano Observatory Roaring geysers and boiling pools of hot mud betray the sleeping giant beneath: an ancient volcano that lies under nearly half of the state of Wyomoing.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Multnomah Falls offers one of the best places in the Columbia River Gorge National Scenic Area to study geology exposed by floods.
  • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

Countries such as Japan and Iceland are especially famous for hot spring baths. Geothermal areas are also an environmentally friendly source of energy, and Iceland takes advantage of this very well.
.Yellowstone National Park is probably the best known example of a geothermal area, as molten magma lies not far beneath its 640,000 year-old caldera.^ Yellowstone National Park First established as a National Park in 1872, Yellowstone remains America's best-known National Park for its geothermal features, array of wildlife and stunning scenery.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Santa Barbara Island lies far south of the other four park islands.
  • Webchat 23 September 2009 4:43 UTC www.rain.org [Source type: General]

^ Lake Toba is a large caldera formed by volcanic and tectonic processes, and was the site of the world's most recent supervolcano 74,000 years ago.

.New Zealand, with its volcanoes in the North Island, is also known for extensive geothermal areas.^ They are now known as Novy Tolbachik or New Tolbachik volcano.
  • Kamchatkan volcanoes 3 February 2010 19:019 UTC maurice.strahlen.org [Source type: FILTERED WITH BAYES]

^ Decade Volcanoes Website A site giving news, updates, online tours and photos for several well-known volcanoes.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ The current lake volume is large enough that it will influence the next phase of eruptive activity from the volcano and result in a new hazard to people visiting the island.

Stay Safe

.If you are intending to venture into an area containing a highly active volcano, be aware that you are entering a potential hazard zone. Depending on the level of activity, the hazard zone may extend for several dozen kilometres, and there is the serious potential for pyroclastic flows and flying volcanic bombs, which are larger pieces of rocks thrown up by eruptions.^ He notes that examining rocks can tell you when the volcano was last active.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ There is potential for a significant eruption.

^ "What do you think the odds are against an eruption up there?
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

.Volcanic bombs can be up to the size of a soccer ball or even larger - enough to kill an unprotected person.^ Nope, hes a Capitalist, and thats enough, even if hes had roughly forty seconds of screentime up til now.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

.Pyroclastic flows are clouds of red-hot ash and other volcanic debris that rush downslope from their source vents.^ A hot, heavy ash cloud rolls above and races ahead of the flow.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Earlier, Hendrasto said that historically the volcano's eruptions have involved ash, smoke and small pieces of volcanic debris.

^ Glowing streaks of red from the pyroclastic flows have created nighttime spectacles visible across much of the island.

.They are some of the most dangerous parts of volcanic eruptions, as the temperature inside a pyroclastic flow can reach 400-700°C (~750-1300°F) and can reach speeds of up to 150 km/h (93 mph).^ Pyroclastic flows or surges are extremely dangerous.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Temperatures inside range from 200 to 700 degrees C. At night they sometimes glow red, hence the old name "glowing clouds."
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Pyroclastic flows also occurred to the northwest approx 2 km down Tyers Ghaut on the 25th of January.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

.Obviously, this means they can literally incinerate everything flammable in their path and then bury the area in hot ash.^ They bury, shatter, or carry away anything in their path.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

.Other associated hazards like volcanic ashfall and lahars (volcanic mudflows) can extend for hundreds of kilometres more.^ South Sister, Broken Top, Mount Jefferson, and several other peaks have a more complex volcanic history.
  • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

^ When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter.

^ Sections include: Eruptive History, Geological History, Geological Evolution, Volcanic Hazards, and more.
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

.Also, volcanic ash tends to stop aircraft and vehicle engines, so transportation in the area may be restricted or disrupted.^ Jones wants NPG, who I guess runs the citys public transportation, to temporarily stop running the subway trains in this area.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ Volcanic ash is falling and combining with torrential rain and high winds in the area.

.Public safety authorities may order hazard areas evacuated and would normally prefer that the casual tourist stay well away.^ Visitors must stay well away from the volcanic steam clouds which contain hydrochloric acid and glass particles.
  • Kilauea Volcano Eruption Update & Information 3 February 2010 19:019 UTC www.volcanogallery.com [Source type: FILTERED WITH BAYES]

^ Authorities evacuated about 100 people from the area.

^ Authorities ordered 116,000 people living along the fertile slopes to evacuate, but many have refused, saying they need to tend to their crops and animals.

.Unless you have some very genuine reasons for going to these places, the best advice is to stay away and watch it from the safety of your home on the TV news.^ Unless youre really going to surprise us by either killing off Brosnan or his new love (Linda Hamilton, presumably, as shes the female lead) or actually lending some depth to the characterizations, well, wed dont give a rats ass.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ Don't forget the timezone; it will be night-time in some of these places.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Not only will you have to convince people to evacuate their homes, but you will also be putting your life in danger as well."
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

.When active volcanoes are not erupting (in other words, simply dormant), many of them can be approached reasonably closely in safety.^ Redoubt and many other volcanoes.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Io, Jupiter's Volcanic Moon This moon of Jupiter caught everyone by surprise when the space probe Voyager passed by: it had active, erupting volcanoes!
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ Stratovolcanoes , also called composite volcanoes , form grand, steep mountains that may remain dormant for long periods before erupting.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

.However, when visiting active volcanic areas, there are still plenty of hazards even in dormant volcanic areas.^ April 2005 deep volcanic = 7 events ; shallow volcanic = 5 events 16 April 2005 deep volcanic = 2 events ; shallow volcanic = 8 events 17 April 2005 deep volcanic = 0 events ; shallow volcanic = 2 events 18 April 2005 deep volcanic = 0 events ; shallow volcanic = 1 events It is still forbidden to visit the summit crater of Anak Krakatau volcano.

.New lava flows may still be very hot for months or even years afterwards and may be only covered with a thin crust of solid rock.^ Only five month later, in may, the river broke through and washed away this locality.
  • Kamchatkan volcanoes 3 February 2010 19:019 UTC maurice.strahlen.org [Source type: FILTERED WITH BAYES]

^ Soon only the driver and NPG are left in the train as the lava flows along under the train.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ Last evening, CD officials reported lava continuing to advance and burn forest down the west side of the TEB flows on the pali.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

.Old lava flows can be as sharp as broken glass, so wearing a good pair of shoes or hiking boots are a must.^ Much of the cone is mantled by lava flows less than 200 years old.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

^ About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

Even geothermal areas can be hazardous. .Many of the hazards encountered in geothermal areas are similar to volcanic hazards, because both arise from similar geological mechanisms.^ Sections include: Eruptive History, Geological History, Geological Evolution, Volcanic Hazards, and more.
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

^ HAZARD ALERT: The lava delta and adjacent areas both inland and out to sea are some of the most hazardous areas on the flow field.
  • Kilauea Volcano Eruption Update & Information 3 February 2010 19:019 UTC www.volcanogallery.com [Source type: FILTERED WITH BAYES]

^ Three well-known areas on the Moon interpreted as important volcanic complexes are: Aristarchus plateau, and the Marius Hills and Rumker Hills (both located in Oceanus Procellarum).
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

.Hot springs and mud pools can be boiling hot, acidic or downright poisonous, hence do not even try to take a dip or approach unless it is absolutely safe to do so.^ Yellowstone Volcano Observatory Roaring geysers and boiling pools of hot mud betray the sleeping giant beneath: an ancient volcano that lies under nearly half of the state of Wyomoing.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ These walls of boiling hot mud have the consistency of concrete and can move at the speed of a freight train, overflowing riverbanks and sweeping away roads and towns.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

^ We cut to two Innocent Young Lovers skinny-dipping in the local hot springs.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

.Geysers are a common feature of major geothermal areas, and can erupt hot water or mud unexpectedly.^ The Norris Back Basin has been closed since July 23 due to the formation of new mud pots, changes in geyser activity and much higher ground temperatures, as hot as 200 degrees in some areas.

^ What looks like a gray river is actually superheated mud and volcanic material mixed with water, and it's boiling hot.
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

.Landslides are also common, as even volcanic rock can become weakened over time with acidic fumes seeping out of fumaroles (steam/gas vents) or hot springs.^ A second vent later opened near the southern summit, piggy-backing its lava and tephra over the previously erupted volcanic rocks.
  • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

^ In contrast to the mostly andesitic Acatenango volcano, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

^ Increased fumarolic activity is common on the warmest days in the summer when snow melts in the crater and more steam is produced.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

.Noxious gases may come out of vents or similar holes in the ground and may be concentrated in enclosed low-lying spaces such as caves, manholes, and pool enclosures.^ Lava rises from depth at this location, but is normally out of view due to the low shield built over the vent.
  • Kilauea Volcano Eruption Update & Information 3 February 2010 19:019 UTC www.volcanogallery.com [Source type: FILTERED WITH BAYES]

^ "Its coming right up out of the ground itself," he notes in a bewildered fashion, although he doesnt explain exactly where else it would come from.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

.Carbon dioxide, a byproduct of volcanic activity, is notorious for this and can kill swiftly with little or no warning.^ In the last weeks emissions of Sulphur Dioxide, no significant fumarolic activity have generally not been detected.
  • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

^ A volcano erupted Saturday with little warning on a remote Aleutian island, sending residents of a nearby ranch fleeing from falling ash and volcanic rock.

Active Volcanoes

.A selection of some of the more active and/or better known volcanoes in the world today.^ They then synthesize their knowledge by creating and presenting reports about currently active volcanoes around the world."
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

^ EARTHS ACTIVE VOLCANOES http://www.geo.mtu.edu/volcanoes/world.html Lists Earths active volcanoes by geographical region.
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

^ Your job in this WebQuest is to explore the active volcanoes of the world and discover how these volcanoes are related.
  • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

Some of these can still be explored from up close.
  • Kilimanjaro in Tanzania is Africa's tallest peak at 5895 m (19,340 ft). .It has a series of concentric summit craters apparently less than 10,000 years old and may have last erupted less than 2000 years ago.^ Mount Jefferson last erupted more than 20,000 years ago.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    ^ Much of its > 530,000 year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Activity at the Kita-dake summit cone ended about 4,850 years ago, after which eruptions took place at Minami-dake.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    .The name Kilimanjaro means "shining mountain" in Swahili, no doubt due to the once-extensive glaciers which are unfortunately disappearing rapidly each year.
  • Ol Doinyo Lengai ("Mountain of God" in the Masai tongue), in Tanzania, is the only volcano on Earth that erupts natrocarbonatite lava.^ Volcano erupts after 9000 years .
    • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

    ^ The Siskiyou Mountains were not heavily glaciated in the last ice age and served as a refuge for species whose habitat disappeared under tons of continental ice.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    ^ Basaltic lava erupts at no less than about 1100 degrees C. Basalt is a very fluid lava; it is likely that tongues of lava advanced at an average of 5 kilometers/hour -- faster than most animals can run.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    This type of lava emerges black, cools to grey, and oxidizes to white.
  • Mount Cameroon The only volcano outside of Europe to have records of an erruption before the Common Era in 5 BC. It remains active today, with its most recent erruption in 2000.

Asia

Indonesia

Mount Semuru erupting in 2004
Mount Semuru erupting in 2004
.With 167 known active volcanoes, Indonesia is the world's most volcanic country by far.^ Come visit the most active Volcano in the World.
  • Kilauea Volcano Eruption Update & Information 3 February 2010 19:019 UTC www.volcanogallery.com [Source type: FILTERED WITH BAYES]

^ It is also one of the most active volcanoes in the Aleutians.

^ Io, Jupiter's Volcanic Moon This moon of Jupiter caught everyone by surprise when the space probe Voyager passed by: it had active, erupting volcanoes!
  • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

Volcano Adventure Indonesia, Sukapura, tel. +62-335-581439 , +62-81319090225, .[1] runs specialist volcano tours all around the country.^ The Laima volcano is part of a chain of around 2,000 in the country [EPA] .

.
  • Mount Bromo in East Java is known for its unreal scenery, especially with Mount Semeru, Indonesia's third highest active volcano nearby.
  • Krakatoa in West Java famously exploded so violently in 1883 that the sound was heard 5,000 km away and global temperatures dipped by over a degree.
  • Mount Batur in Bali is a very accessible active volcano which takes just 2 hours to climb.
  • Mount Rinjani in Lombok is Indonesia's second highest volcano with a stunning crater lake.^ Crater Lake lies inside the top of an ancient volcano known as Mount Mazama.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    ^ Yellowstone National Park First established as a National Park in 1872, Yellowstone remains America's best-known National Park for its geothermal features, array of wildlife and stunning scenery.
    • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

    ^ N evado del Huila, the highest active volcano in Colombia, is an elongated N-S-trending volcanic chain mantled by a glacier icecap.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    .For much of 2009 the summit of the mountain was closed to the public due to eruptive activity.
  • Mount Tambora in Sumbawa is one for the truly adventurous.^ A s of the 1st of January, Mount Etna is one of the most active volcanoes in the world and is in an almost constant state of activity.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ The present activity in Galeras continues showing a development unstable, similar to the registered one before the occurrence of some of the recent eruptive events.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Due to its history of recent activity and nearby population, Mount Etna has been designated a Decade Volcano by the United Nations.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    .Only about 50 visitors a year make it to this very remote volcano.^ Construction of Meseta volcano dates back to about 230,000 years and continued until the late Pleistocene or early Holocene.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Only about 50 persons live on the sparsely populated island.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ The caldera enclosing Karymsky volcano formed about 7600-7700 radiocarbon years ago; construction of the Karymsky stratovolcano began about 2000 years later.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    In 1814 Tambora was 4,200 metres high. It erupted with such force the following year that 1,400 metres was lost from its top.

Elsewhere

.
  • Mount Aso on the island of Kyushu in Japan, is one of the largest active volcanoes in the world with the largest caldera.
  • Mount Fuji in central Japan near Tokyo, is Japan's highest and most beautiful volcano.^ K liuchevskoi is Kamchatka's highest and most active volcano.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Come visit the most active Volcano in the World.
    • Kilauea Volcano Eruption Update & Information 3 February 2010 19:019 UTC www.volcanogallery.com [Source type: FILTERED WITH BAYES]

    ^ The archipelago nation has the world's highest number of active volcanoes.

    .It is also the most climbed mountain in the world because so many people climb it to view the sunrise from its summit crater.
  • Mayon Volcano, near Legazpi City in the Philippines, described as the world's most perfect volcano cone.^ Satellites can detect volcanoes that are more than 1500 m high because the mass of the submerged mountains causes gravity to pull the water in around them.

    ^ PHILIPPINES - PREPARE FOR IMMEDIATE EVACUATION authorities on Sunday warned residents living near Mount Mayon, as lava flowed past the volcano's six-kilometer permanent danger zone.

    ^ Kilauea Iki was another vent that broke out near the summit of Kilauea Volcano, in a crater right next to the caldera.
    • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

    .Mayon’s last fatal eruption was in 1993.
  • El Teide in Tenerife, is the highest active volcano in the Canary Islands at 3715 m (12,188 ft).^ N evado del Huila, the highest active volcano in Colombia, is an elongated N-S-trending volcanic chain mantled by a glacier icecap.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ The volcano, whose name means "Child of Krakatau," formed in the Sunda Strait close to Java island after Mount Krakatau's legendary eruption in 1883.

    ^ Includes eruption summaries, reports, data and references to most volcanoes that have been active over the past 11,000 years.
    • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

    .A flank vent at El Teide was observed erupting by Christopher Columbus and his crew in 1492.
  • Vesuvius near Naples in Italy is an active (but presently "dormant") volcano.^ Io, Jupiter's Volcanic Moon This moon of Jupiter caught everyone by surprise when the space probe Voyager passed by: it had active, erupting volcanoes!
    • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

    ^ Stratovolcanoes , also called composite volcanoes , form grand, steep mountains that may remain dormant for long periods before erupting.
    • Volcanoes Are Hot Stuff 3 February 2010 19:019 UTC www.squidoo.com [Source type: FILTERED WITH BAYES]

    ^ The closest active volcano to the earthquake is Kunlun in Western China, which last erupted in 1951.

    .It has not been smoking since it last erupted in 1944, but it is still very closely monitored because of its seriously hazardous proximity to Naples, which is southern Italy's largest city.
  • Stromboli in the Aeolian Islands of Italy and Mount Etna in Sicily, Italy are two of Italy's most active volcanoes.^ It is also one of the most active volcanoes in the Aleutians.

    ^ Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BC. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Chile's Chaiten Volcano, which erupted spectacularly last year, spewed a vast cloud of ash on Thursday in what appeared to be a partial collapse of its cone.

    At 3350 m (10,991 ft), Etna is Europe's highest volcano. .Stromboli has been in near continuous activity since at least the time of the Ancient Greeks and has been billed as the "Lighthouse of the Mediterranean".
  • Nisyros in the Greek Dodecanese islands is mildly active with smoking fumaroles.^ Fumarolic activity continues at the central and SW summit craters.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterised its eruptions throughout much of historical time.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    .It is possible to walk into the crater floor for a closer look.
  • Santorini in the Aegean Sea, is probably Greece's most famous volcano because of its eruption that destroyed the Minoan civilization over 3,600 years ago.^ Its most recent eruption was about 1,300 years ago.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    ^ Activity at the Kita-dake summit cone ended about 4,850 years ago, after which eruptions took place at Minami-dake.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ We use a short cup to hold the baking soda because we are looking at the flows and not at constructing a volcano model.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    It is still active, for it last erupted in 1950 out of Nea Kameni ("New Burnt" in Greek), an island made up of lava flows in the middle of the caldera bay.
  • Mount St. Helens, in Washington State, USA, is famous for its May 18, 1980 eruption. .Since late 2004, it has been erupting once again, but not nearly as violently - this time, a new lava dome is slowly being extruded in its crater.
  • Popocatepetl, near Mexico City, often has a volcanic plume above its crater which is 5,450m high.^ Mexico's Volcano of Fire, also known as the Colima volcano, is seen in a time exposure photograph during an explosion as lava and hot rocks flow down its sides and lightning flashes over its crater late June 1, 2005.

    ^ A s of the 29th of January, the Kamchatkan Volcanic Eruption Response Team (KVERT) reported that activity of the volcano continues: a new viscous lava flow effuses at the lava dome.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ A rhyolitic, 962-m-high obsidian lava dome occupies much of the caldera floor.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    .The name means "smoking mountain" in the native Nahuatl language.
  • Soufriere Hills volcano on Montserrat, previously considered dormant, began erupting again in 1995, forcing the closure of the southern half of the island (including its capital and airport in 1997).^ Latest news of the eruption of volcano SOUFRIERE HILLS on Montserrat in the Caribbean.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ T he complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ There is no access to Zone C and only daytime access (0630 hrs to 1730 hrs) to part of Zone B. T he complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    .It is still active, though mostly a nuisance seeping lava and spewing ash into the air.
  • Cotopaxi in Ecuador, often misquoted as being the highest volcano in the world ( despite its elevation of 5911 m (19, 393 ft), it does not even make the top ten list of highest active volcanoes - see this list here), is still one of South America's most spectacular volcanoes.
  • Arenal in Costa Rica can be viewed lighting up the night sky with its highly frequent eruptions.
  • Mount Ruapehu, Mount Ngauruhoe and Mount Tongariro in New Zealand's Tongariro National Park.^ Latest news of the eruption of volcano FUEGO in Guatemala.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Aleutian volcano spews ash 50,000 feet into the air .

    ^ T he eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    .Ruapehu, New Zealand's highest volcano, has a crater lake that forms and fills when the volcano is not erupting.
  • White Island, also in New Zealand, is the most active volcano in that country and is a volcanic island in the Bay of Plenty southeast of Auckland.^ K liuchevskoi is Kamchatka's highest and most active volcano.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Sunday, August 10, 2003 New crater lake forms at White Island Volcano...

    ^ It is also one of the most active volcanoes in the Aleutians.

    .Organized tours are operated out to this volcano.
  • Kilauea in the Big Island of Hawaii, has been erupting continuously out of its flank vent, known as Pu'u O'o ("Hill of the O'o bird" in the native Hawai'ian language) since 1983.
  • Mauna Loa, also in Hawaii, is the state's highest historically active volcano and is topped by the Moku'aweoeo Caldera.^ K ilauea volcano, which overlaps the east flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ Update news of the continuing eruption of volcano KILAUEA in Hawaii.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ VOLCANO VILLAGE http://volcanovillage.com/ " Located on the Big Island of Hawaii, 28 miles from Hilo at an elevation of 3700 feet, Volcano Village sits at the entrance to the Hawaii Volcanoes National Park, home of Kilauea and Mauna Loa volcanoes; Kilauea being the most active volcano on the planet.
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    .It is also the largest volcano by volume in the world.^ Chile's chain of some 2,000 volcanoes is the world's second-largest after Indonesia's.

    ^ The earthquake was located about 100 km NE of Manam volcano, the site of the largest eruption in the world in 2004.

    .Don't be fooled by its gentle slopes - with its highest point at 4170m/13,683 ft), the altitude can be hard on inexperienced hikers and its summit is often covered in snow during the winter.
  • Mauna Kea is the highest volcano in Hawaii at 4205 m (13,796 ft), and is pockmarked with cinder cones.^ Many have summit cinder cones.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    ^ A lower level ash plume covering a large area drifted south at an altitude of 18,000 ft.

    ^ The highest point on the volcano, Paulina Peak with an elevation of 7,984 feet, is about 4,000 feet higher than the terrain surrounding the volcano.
    • CVO Menu - America's Volcanic Past - Oregon 28 January 2010 1:01 UTC vulcan.wr.usgs.gov [Source type: FILTERED WITH BAYES]

    Its high elevation is also a magnet for astronomers with their giant telescope facilities - and even skiers.
  • Hale'akala ("House of the sun" in Hawai'ian), is the tallest volcano on the island of Maui, and is renowned for its erosional crater and the cinder cones nestled inside.

Travel agencies

.The following travel agencies specialize in volcano tourism.^ The Yasur volcano on Tanna Island in the south of the archipelago was "of more concern for tourists and tourism agencies," who visit it frequently, she noted.

  • Volcano Adventure Indonesia, Sukapura, Indonesia, tel. +62-335-581439 , +62-81319090225, [2]. Tours to Mount Bromo and elsewhere in Indonesia.
  • VolcanoDiscovery, Germany, tel. +49-2241-2080175, +30-2107522310, [3]. .This tour operator is specialized on international volcanoes and one of its most important programs are provided for Indonesian volcanoes.^ It is also one of the most active volcanoes in the Aleutians.

    ^ T he eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    ^ It has one of Earth's few long-lived lava lakes and is the most active volcano in Antarctica.
    • News 3 February 2010 19:019 UTC www.intlvrc.org [Source type: FILTERED WITH BAYES]

    The tours are trekking & photography tours with small groups and an intensive personal service. .The tours are usually about 7-14 days.
  • Volcano Guide in Indonesia, Tangerang, Indonesia, +62-8111875236, [4].^ Students will participate in a virtual reality tour by the use of my web pages to explore and learn about volcanoes in Mexico."
    • WEBSITES ON EARTHQUAKES & VOLCANOES 3 February 2010 19:019 UTC www.cumbavac.org [Source type: General]

    specialist in Volcano Tour and Volcano Expedition also some Jungle Trekking In Indonesia, all of the trip is private tours in Indonesia.
This is a usable article. It has information for getting in as well as some complete entries for restaurants and hotels. An adventurous person could use this article, but please plunge forward and help it grow!

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

.VOLCANO, an opening in the earth's crust, through which heated matter is brought, permanently or temporarily, from the interior of the earth to the surface, where it usually forms a hill, more or less conical in shape, and generally with a hollow or crater at the top.^ The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months.

^ The volcano remains a popular destination for climbers, who try to reach the top to peer into the crater.

^ The Soufriere Hills volcano became active in 1995, and more than half the territory's 12,000 inhabitants moved away.

This hill, though not an essential part of the volcanic mechanism, is what is commonly called the volcano. The name seems to have been applied originally to Etna and some of the Lipari Islands, which were regarded as the seats of Hephaestus, a Greek divinity identified with Vulcan, the god of fire in Roman mythology. All the phenomena connected directly or indirectly with volcanic activity are comprised under the general designation of vulcanism or vulcanicity - words which are also written less familiarly as volcanism and volcanicity; whilst the study of the phenomena forms a department of natural knowledge known as vulcanology. Vulcanicity is the chief superficial expression of the earth's internal igneous activity.
.It may happen that a volcano will remain for a long period in a state of moderate though variable activity, as illustrated by the normal condition of Stromboli, one of the Lipari Islands; but in most volcanoes the activity is more decidedly intermittent, paroxysms of greater or less violence occurring after intervals of comparative, or even complete, repose.^ It is also one of the most active volcanoes in the Aleutians.

^ Hunter Island, along with Matthew Island are the most southerly active volcanoes in Vanuatu.

^ Clear sight lines have made it possible to gaze at Rainier and appreciate it less as an intermittent aesthetic pleasure and more for what the U.S. Geological Survey (USGS) warns that it really is.

If the period of quiescence has been very protracted, the renewed activity is apt to be exceptionally violent. .Thus, Krakatoa before the great eruption of 1883 had been dormant for something like two centuries, and it is believed that the Japanese volcano Bandaisan previously to the gigantic outburst of 1888 had been silent for more than a thousand years.^ "More like ten thousand to one."
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months.

^ The volcano, whose name means "Child of Krakatau," formed in the Sunda Strait close to Java island after Mount Krakatau's legendary eruption in 1883.

A volcano may indeed remain so long dormant as to be mistaken for one completely extinct. .The volcanoes of central France are regarded as extinct, inasmuch as no authentic historical record of any eruption is known, but there are not wanting signs that in some parts of this volcanic region the subterranean forces may yet be slumbering rather than dead.^ But if there are more eruptions, we may have ash over central Europe," he said.

^ There have been no deaths associated with the eruptions that began earlier this month, but thousands of villagers have been evacuated from the area.

^ Earlier, Hendrasto said that historically the volcano's eruptions have involved ash, smoke and small pieces of volcanic debris.

Table of contents

Premonitory Symptoms

.A volcanic eruption is usually preceded by certain symptoms, of which the most common are local earthquakes.^ The risk of a large volcanic eruption resulting from the recent Sumatra earthquakes is not great, but nevertheless should not be ignored.

^ The earthquakes were followed at 2150 GMT by a sequence of volcanic tremors that confirmed an eruption was underway.

The mountain, or other eruptive centre, may be thrown by internal activity into a state of tremor; the tremors perhaps continuing intermittently for months or even years, and becoming more frequent and violent as the crisis approaches. .At first they are usually confined to the volcano and its immediate neighbourhood, but may subsequently extend to a considerable distance, though probably never developing into earthquakes of the first magnitude.^ The magnitude 6.8 earthquake hit 160 km WNW of Hunter Island Volcano in Vanuatu.

^ You know, even if people dont know why volcanoes and earthquakes occur, they know they happen.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ No signs of an immediate eruption were reported as of posting time though residents affected by ash fall and pyroclastic materials from the volcano were told they should evacuate.

The sudden opening of a subterranean crack, by rupture of a rock under strain, or the rapid injection of lava into such a fissure, will tend to produce a jar at the surface. .For at least sixteen years before the first recorded eruption of Vesuvius in A.D. 79 earthquakes had been frequent in the Campania and had wrought havoc in the cities of Herculaneum and Pompeii.^ Seismic activity on 15-16 April from 1800-0600 hr recorded 79 volcanic earthquakes, and 2 gas emissions.

^ Hydro-acoustic monitoring is the first system of surveillance that has been performed at the crater lake and has revealed intense gas bubbling a year before seismic precursor records of the 1990 eruption.

^ Ashes from that eruption, one of the most devastating natural disasters in recorded history, were carried by upper level winds as far away as New York City.

.Again, the formation of Monte Nuovo, near Pozzuoli, in 1538, was heralded by local earthquakes beginning several years in advance of the eruption.^ Yemeni officials are linking the eruption to several small earthquakes which they say hit the island on Sunday morning.

.So too in recent years many volcanic outbursts have been preceded by a succession of earthquakes; but as volcanoes are frequently situated in areas of marked seismic activity, the shocks antecedent to an eruption may not, unless exceptionally violent, receive much attention from local observers.^ Seismic activity: 14th April, 35 volcanic earthquakes in 6 hours.

^ The local seismic stations daily register up to 100 earthquakes in the volcano area.

^ Talang is on a list of volcanoes identified as eruption risks by John Seach following the large earthquakes in the region.

It commonly happens that a volcanic outburst is announced by subterranean roaring and rumbling, often compared to thunder or the discharge of artillery underground. Other precursory symptoms may be afforded by neighbouring springs, which not unusually flow with diminished volume, or even fail altogether. Possibly fissures open underground and drain off the water from the springs and wells in the immediate locality. Occasionally, however, an increased flow has been recorded. In some cases thermal springs make their appearance, whilst the temperature of any existing warm springs may be increased, and perhaps carbon dioxide be evolved. .A disturbed state of the atmosphere is by no means a constant forerunner of an eruption, some of the greatest outbursts having occurred in a period of atmospheric stability: indeed the air is often felt to be close and still.^ The volcano, whose name means "Child of Krakatau," formed in the Sunda Strait close to Java island after Mount Krakatau's legendary eruption in 1883.

^ No casualties were reported after the afternoon eruption of the 12,540-foot (3,860-meter) Colima volcano in the western state of the same name.

.Immediately before a renewed outburst in an old volcano, the floor of the crater is generally upheaved to a greater or less extent, whilst the discharge of vapour from any fumaroles is increased.^ The Volcanological Survey of Indonesia reports seismicity has increased at the volcano, and sulfuric gas was strongly smelt near Ratu Crater.

.Where a crater has been occupied by water, forming a crater-lake, the water on the approach of an eruption becomes warm, evolves visible vapour, and may even boil.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

^ Sunday, August 10, 2003 New crater lake forms at White Island Volcano...

^ He said water samples from the lake would help determine what was happening in the crater and below it.

.In the case of cones which are capped with snow, the internal heat of the rising lava usually causes a rapid melting of the snow-cap, resulting perhaps in a disastrous deluge.^ Jones sends his daughter off with Jaye to the hospital (the lava that spurted on her leg or the resultant pants fire -- has caused a small second-degree burn).
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

It seems probable that by attention to the premonitory symptoms a careful local observer might in many cases foretell an eruption.
It generally happens that a great eruption is preceded by a preliminary phase of feeble activity. Thus, the gigantic catastrophe at Krakatoa on the 27th of August 1883, so far from having been a sudden outburst, was the culmination of a state of excitement, sometimes moderate and sometimes violent, which had been in progress for several months.

Emission of Vapour

Of all volcanic phenomena the most constant is the emission of vapour. .It is one of the earliest features of an eruption; it persists during the paroxysms, attaining often to prodigious volume; and it lingers as the last relic of an outburst, so that long after the ejection of ashes and lava has ceased an occasional puff of vapour may be the only memento of the disturbance.^ As compared to the eruption of 1956, the only one in the history of modern observations, the current eruption started in a more impetuous and powerful way the scientist pointed out.

^ In modern history only one eruption, starting in 1956 was observed.

^ The eruptions forced the evacuation of thousands of villagers and damaged thousands of acres of crops buried under tons of ashes and lava flows.

By far the greatest proportion of the vapour is steam, which sometimes occurs almost to the exclusion of other gaseous products. Such, at least, is the usual and probably correct view, though it is opposed by A. Brun, who regards the volcanic vapours as chiefly composed of chlorides with steam in only subordinate amount. .In the case of a mild eruption, like that occurring normally at Stromboli, the vapours may be discharged in periodical puffs, marking the explosion of bubbles rising more or less rhythmically from the seething lava in the volcanic cauldron.^ The last eruption of Karthala volcano was in 1991 when an explosion occurred at Choungou-Chahal crater.

^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

.S. Wise observed at the volcano of Sangay, in Ecuador, no fewer than 267 explosions in the course of an hour, the vapour here being associated, as is so often the case, with ashes.^ Earlier this month, authorities evacuated about 100 families from the slopes of the Tungurahua volcano in central Ecuador after it showered villages with flaming rocks and ash.

^ Ecuador's Reventador Volcano Spews Ash Mar 30 11:52 PM US/Eastern .

^ There have been no lava flows since the volcano began spitting out ash in December, he said.

During a violent eruption the vapour may be suddenly shot upwards as a vertical column of enormous height, penetrating the passing clouds. For a short distance above the vent the superheated steam sometimes exists as a transparent vapour, but it soon suffers partial condensation, forming clouds, which, if not dispersed by winds, accumulate over the mountain. .When the vapour is free from ash it forms rolling balls of fleecy cloud, but usually it carries in mechanical association more or less finely divided lava as volcanic dust and ashes, whereby it becomes yellow, brown, or even black, sometimes as foul as the densest smoke.^ Earlier, Hendrasto said that historically the volcano's eruptions have involved ash, smoke and small pieces of volcanic debris.

^ Garae said hundreds of inhabitants of nearby Paama Island fled from the falling ash, dense smoke and lava flows from Lopevi, she said.

^ "The lava is spewing hundreds of feet into the air, with the volcanic ash also 1,000 feet in the air."

In a calm atmosphere the dust-laden vapour may rise in immense rings with a rotatory movement, like that of vortex-rings. Frequently the vapours, emitted in a rapid succession of jets, form cumulus clouds, or are massed together in cauliflower-like forms. The well-known " pine-tree appendage " of Vesuvius (pino vulcanico), noted by the younger Pliny in his first letter to Tacitus on the eruption in the year 79, is a vertical shaft of vapour terminating upwards in a canopy of cloud, and compared popularly with the trunk and spreading branches of the stonepine. .Whilst in some cases the cloud resembles a gigantic expanded umbrella, in others it is more mushroom-shaped.^ It turns out that some of the other town leaders (all men, natch) want to cover things up, in case the Evil Capitalist decides not to invest in the town.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

In a great eruption, the height of the mountain itself may appear dwarfed by comparison with that of the column of vapour. During the eruption of Vesuvius in April 1906, the steam and dust rose to a height of between 6 and 8 m. .At Krakatoa in 1883 the column of vapour and ashes reached an altitude of nearly 20 m.; whilst it was estimated by some authorities that during the most violent explosions the finely divided matter must have been carried to an elevation of more than 30 m.^ When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter.

^ Scientists at the University of Colima said Sunday's explosion was 20 percent larger than the May 30 eruption.

^ Since its formation some 6,000 years ago, Klyuchevskaya has seen few periods of inactivity, and the volcano is estimated to have experienced more than 100 flank eruptions in the past 3,000 years.

.The emission of vast volumes of vapour at high tension naturally produces much atmospheric disturbance, often felt at great distances from the centre of eruption.^ The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months.

Electrical Excitement

It is probably to the uprushing current of vapour that much of the electrical excitement which invariably accompanies an eruption may be referred. .The friction of the steam rushing in jets through the volcanic vent must produce electrical disturbance, and indeed an active volcano has been aptly compared to a hydroelectric machine of gigantic power.^ The volcanic system is considered to be among the most active and potentially the most destructive of the volcanoes in Mexico.

^ Awesome power of Iceland volcano The eruption has been spectacular (Image: Dr Matthew Roberts) A spectacular volcanic eruption under an Iceland glacier has forced airlines to divert flights to avoid flying through gas emissions from the blast.

^ Large earthquakes are capable of disturbing volcanic systems, and a watch should be kept over the volcanoes of Sumatra and Andaman Islands for change in activity.

.Another cause of excitement may be found in the mutual friction of the ejected cinders and ashes as they rise and fall in showers through the air.^ The health department has warned residents to stay indoors as the ash may cause respiratory problems and eye and skin irritation.

^ A plume of ashes and smoke rises from the Chaiten volcano some 1,200 km south from Santiago, Chile on May 2, 2008.

^ Here comes that greedy helicopter pilot, offering to fly people out through the extremely heavy falling ash for $15,000 a head, in cash.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

Much trituration of volcanic material may go on in the crater and elsewhere during the eruption, whereby the solid lava is reduced to a fine dust. .Other means of generating electricity are found in the chemical reactions effected in the volcano and in the sudden condensation of the emitted vapour.^ On the other hand due to the climatic conditions that stay in the zone of the volcano is possible the generation of mud flows or "lahars", thus it is necessary that the population stays letter to the messages that emit means authorized.

L. Palmieri, in the course of his investigations at the observatory on Vesuvius, found that the vapours free from cinders carried a positive charge, whilst the cinders were negative.
The electrical phenomena attending an eruption are often of great intensity and splendour. .The dark ash-laden clouds of vapour are shot through and through by volcanic lightning, sometimes in rapid horizontal flashes, then in oblique forked streaks, or again in tortuous lines compared to fiery serpents, whilst the borders of the cloud may be brilliant with electric scintillations, often forming balls and stars of fire.^ A cloud of debris soared as high as 20 miles (32 km) into the air when the volcano erupted in May and was kept aloft by the pressure of constant eruptions for weeks, covering towns in neighboring Argentina with volcanic ash.

^ This plumes dark color suggests that it consists primarily of volcanic ash.

^ The most useful instrument in observing the earth is employing a form of a very large radio telescope that stretches from border to border the electrical power grid.

During the great eruption of Krakatoa remarkable phenomena were observed by ships in the Strait of Sunda, luminous balls like " St Elmo's fire " appearing at the mast-heads and the yard-arms, whilst the volcanic mud which fell upon rigging and deck was strongly phosphorescent.
.Quite distinct from any electrical phenomena is that intermittent reddish glare which is often seen at night in clouds hanging over an active crater, and which is simply a glow due to reflection from ,the incandescent lava and stones in the volcanic cauldron below.^ Visual observations of the volcano at the end of March by John Seach recorded a strong night glow at Benbow, and the sound of bubbling lava could be heard deep in the crater, accompanied by continuous light-brown ash emissions.

Volcanic Rain and Mud

.The condensation of the vast volumes of steam exhaled during an eruption produces torrents of rain, which, mingling to a greater or less extent with the volcanic ashes, forms a hot muddy stream known in Italy as lava d'acqua and lava di fango, and in South America as moya. Deluges of such mud-lava may rush violently down the mountain-side and spread over the neighbouring country with terribly destructive effect, whence they are greatly dreaded by those who dwell at the base of a volcano.^ On Monday, the 5,850-feet volcano shot out at least 30 bursts of lava and hot ash, said Saut Simatupang, chief researcher at the government's vulcanology agency.

^ For instance, as when Jaye didnt see the ash tower, a post-production effect of a huge tower of lava is shown fountaining up from the La Brea Tar Pits.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ That flurry of activity in turn came a week after lava spewed down one of its sides.

.The solidified volcanic mud, often mingled with larger fragments of lava, is known as duf f or tufa. Herculaneum was buried beneath a flood of mud swept down from Vesuvius during the Plinian eruption of 79, and the hard tufaceous crust which thus sealed up the illfated city came in turn to be covered by lava-flows from subsequent eruptions: hence the difficulty of excavating at Herculaneum compared with similar work at Pompeii, where there was probably much less mud, since the city, having been at a greater distance from the volcanic centre, was overwhelmed in great measure by loose ashes, capable of removal with comparative ease.^ Demolition teams are thus sent to intersect the route of the lava (theres not enough time or manpower to evacuate Cedars Sinai) and create a trench that will redirect the flow towards Ballona Creek, which feeds into the ocean.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ Since the flow of lava looks exactly like a, well, flow of lava, we cant quite understand why hes having this much trouble describing the scene.
  • Dante's Peak & Volano:  A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]

^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

It sometimes happens that volcanic mud is formed by the mingling of hot ashes not directly with rain but with water from streams and lakes, or even, as in Iceland, with melted snow. .A torrent of mud was one of the earliest symptoms of the violent eruption of Mont Pele in Martinique in 1902. This mud had its source in the Etang Sec, a crater-basin high up on the S.W. side of the mountain.^ The 800-metre-wide plateau inside the crater dropped 300 metres during the eruption, and islanders remain on high alert.

^ Mount Karangetang, one of the country's most active mountains, has been at a state of high alert for two weeks.

.By the explosive discharge of ashes and vapours mingled with the water of the tarn there was produced a vast volume of hot muddy matter which on the 5th of May suddenly escaped from the basin, when a huge torrent of boiling black mud, charged with blocks of rock and moving with enormous rapidity, rolled like an avalanche down the gorge of the Riviere Blanche.^ When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter.

^ Part of the volcano's dome collapsed late Saturday, sending a torrent of mud and ash down into the adjacent Tar River Valley and pelting distant houses and buildings with rocks.

^ Gas and hot ash caused snow on the mountain peak to melt, sending mud, rocks and floodwater rushing down the River Paez and destroying at least 20 homes and washing out five bridges, the presidential office said in a statement.

.If a stream of lava obstructs the drainage of a volcano, it may give rise to floods.^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

^ A plume of ashes and smoke rises from the Chaiten volcano some 1,200 km south from Santiago, Chile on May 2, 2008.

Ejected Blocks

.When a volcano after a long period of repose starts into fresh activity, the materials which have accumulated in the crater, including probably large blocks from the disintegration of the crater-walls, have to be ejected.^ Episodes of greater activity have ejected material beyond the crater rim.

^ ECUADOR - Tungurahua volcano April 10, 2002 As of the 8th of April, the Instituto Geofisico (IG), has reported that 10 earthquakes of long period and one continuous tremor activity were registered that to a large extent is correlated with emissions of steam and ash.

^ Stromboli Volcano (Italy) 38.79 N, 15.21 E, summit elevation 926 m, stratovolcano Strombolian activity continues from the northern summit crater.

.If the lava from the last eruption has consolidated as a plug in the throat of the volcano, the conduit may be practically closed, and hence the first effort of the renewed activity is to expel this obstruction.^ He said Thursday's eruption had produced some lava flows that did not extend far from the volcano's crater.

^ The Chilean Web site emol.com is reporting that the volcanos dome, which has built up gradually since Chaitn first erupted last May, partially collapsed.

^ The 2,568 meter Asama, which last had a minor eruption in August last year, is one of the most active volcanoes in Japan.

The hard mass becomes shattered by the explosions, and the angular fragments so formed are hurled forth by the outrushing stream of vapour. When the discharge is violent, the vapour, as it rushes impetuously up the volcanic duct, may tear fragments of rock from its walls and project them to a considerable distance from the vent. Such ejected blocks, by no means uncommon in the early stages of an eruption, are often of large size and naturally vary according to the character of the rocks through which the duct has been opened. .They may be irregular masses of igneous rocks, possibly lavas of earlier eruptions, or they may be stratified, sedimentary and fossiliferous rocks representing the platform on which the volcano has been built, or the yet more deeply seated fundamental rocks.^ Satellites can detect volcanoes that are more than 1500 m high because the mass of the submerged mountains causes gravity to pull the water in around them.

^ Earlier this month, authorities evacuated about 100 families from the slopes of the Tungurahua volcano in central Ecuador after it showered villages with flaming rocks and ash.

^ Earlier, Hendrasto said that historically the volcano's eruptions have involved ash, smoke and small pieces of volcanic debris.

.By Dr H. J. Johnston-Lavis, who specially studied the ejected blocks of Vesuvius, the volcanic materials broken from the cone are termed " accessory " ejecta, whilst other fragmentary materials he conveniently calls " accidental " products, leaving the term " essential " ejecta for plastic lava, ashes, crystals, &c.^ ORIGINAL CAPTION : Superheated ash and lava is visible inside the cone of the Soufriere Hills volcano, which has been active lately, as seen from Olveston, Montserrat, on Jan.

^ "The lava is spewing hundreds of feet into the air, with the volcanic ash also 1,000 feet in the air."

Masses of Cretaceous or Apennine limestone ejected from Somma are scattered through the tuffs on the slopes of Vesuvius; and objects carved in such altered limestone are sold to tourists as " lava " ornaments. Under the influence of volcanic heat and vapours, the ejected blocks suffer more or less alteration, and may contain in their cavities many crystallized minerals. Certain blocks of sandstone ejected occasionally at Etna are composed of white granular quartz, permeated with vitreous matter and encased in a black scoriaceous crust of basic lava.
A rock consisting of an irregular aggregation of coarse ejected materials, including many large blocks, is known as a " volcanic agglomerate." Any fragmental matter discharged from a volcano may form rocks which are described as " pyroclastic." Cinders, Ashes and Dust. - .After the throat of a volcano has been cleared out and a free exit established, the copious discharge of vapour is generally accompanied by the ejection of fresh lava in a fragmentary condition.^ Indonesia officials evacuated 11,000 villagers from around Mount Merapi volcano as it shot out lava and superheated clouds of gas on June 6,2006 .

^ There have been no lava flows since the volcano began spitting out ash in December, he said.

^ Raging lava has spewed out of one of the world's most active volcanos on the French island of La Reunion.

If the ejected masses bear obvious resemblance to the products of the hearth and the furnace, they are known as " cinders " or " scoriae," whilst the small cinders not larger than walnuts often pass under their Italian name of "lapilli" (q.v.). When of globular or ellipsoidal form, the ejected masses are known as " bombs " (q.v.) or " volcanic tears." Other names are given to the smaller fragments. .If the lava has become granulated it is termed " volcanic sand "; when in a finer state of division it is called ash, or if yet more highly comminuted it is classed as dust; but the latter terms are sometimes used interchangeably.^ As lava flows from the Pits, a reporter vainly tries to explain the phenomena without using the terms lava or volcano.
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^ Etna is in an almost constant state of activity, but is not considered particularly dangerous and its slopes are home to farms and vineyards that make use of the rich volcanic soil.

^ But while lava levels inside the crater have subsided, earth tremors have become more frequent.

.The pulverized material, consisting of lava which has been broken up by the explosion, or triturated in the crater, is often discharged in prodigious quantity, so that after an eruption the country for miles around the volcano may be covered with a coating of fine ash or dust, sometimes nearly white, like a fall of snow, but often of greyish colour, looking rather like Portland cement, and in many cases becomirg reddish by oxidation of the ferruginous constituents.^ "It almost looks like lava," he exclaims.
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^ The eruption has also affected tea plantations close to the volcano, which have been covered in ash.

^ Experts at Colima University have said the 12,664 feet volcano's seismic activity has intensified along with explosions and that its lava crust has broken, causing lava to spill over the southwestern slopes.

Even when first ejected the ash is sometimes cocoa-coloured. This finely divided lava insinuates itself into every crack and cranny, reaching the interior of houses even when windows and doors are closed. .A heavy fall of ash or cinders may cause great structural damage, crushing the roofs of buildings by sheer weight, as was markedly the case at Ottajano and San Guiseppe during the eruption of Vesuvius in April 1906. On this occasion the dry ashes slipped down the sides of the volcanic cone like an avalanche, forming great ashslides with ridges and furrows rather like barrancos, or ravines, caused by rain.^ The resident population and guests of the region are advised to limit the time of staying outdoors during ashfalls, as volcanic dust may cause poisoning and other negative consequences.

^ During the late 18th century, continuous volcanic eruptions in Iceland heavily damaged a quarter of the island nation, and blotted out the sun's light for several years.

^ "It was in a high state of eruption because ash was falling on Ambryn and Paama islands, but then ...

The burial of Ottajano and San Ginseppe in 1906 by Vesuvian ejecta, mostly lapilli, has been compared with that of Pompeii in 79.
.Deposits of volcanic sand and ashes retain their heat long after ejection, so that rain will cause them to evolve steam, and if the rain be heavy and sudden it may produce explosions with emission of great clouds of vapour.^ The explosion flung an ash cloud at least 50,000 feet high, said geophysicist Steve McNutt.

^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

^ ECUADOR - Tungurahua volcano April 10, 2002 As of the 8th of April, the Instituto Geofisico (IG), has reported that 10 earthquakes of long period and one continuous tremor activity were registered that to a large extent is correlated with emissions of steam and ash.

.The fall of ash is at first prejudicial to vegetation, and is often accompanied or followed by acid rain; but ultimately the ash may prove beneficial to the soil, chiefly in consequence of the alkalis which it contains.^ Volcanic ash is falling and combining with torrential rain and high winds in the area.

^ There is concern that ash and acid rain has contaminated water supplies in the area.

.The " May dust " of Barbados was a rain of volcanic ash which fell in May 1812 from the eruption of the Soufriere in St Vincent.^ Dust and ash fell in Ternate, around 30 kilometers (20 miles) north of the mountain.

^ Earlier, Hendrasto said that historically the volcano's eruptions have involved ash, smoke and small pieces of volcanic debris.

^ A brief eruption in May of 1994 sent ash to 10.5 km.

It is estimated that the amount of dust which during this eruption fell on the surface of Barbados, Ioo m. distant from the eruptive centre, was about 3,000,000 tons. .The distance to which ash is carried depends greatly on the atmospheric conditions at the time of the eruption.^ Ashes from that eruption, one of the most devastating natural disasters in recorded history, were carried by upper level winds as far away as New York City.

.Ashes from Vesuvius in an eruption in the year 472 were carried, it is said, as far as Constantinople.^ Volcanoes Erupt in Japan and Russia, Spreading Ash Two volcanoes in Japan and another in eastern Russia erupted overnight, spreading ash as far as the Philippines and Vietnam, the Japan Meteorological Agency said on its Web site.

^ Earlier, Hendrasto said that historically the volcano's eruptions have involved ash, smoke and small pieces of volcanic debris.

^ But if there are more eruptions, we may have ash over central Europe," he said.

.During an eruption of Cotopaxi, on the 3rd of July 1880, observed by E. Whymper, an enormous black column of dust-laden vapour was shot vertically upwards with such rapidity that in less than a minute it rose to a height estimated at 20,000 ft.^ Since its formation some 6,000 years ago, Klyuchevskaya has seen few periods of inactivity, and the volcano is estimated to have experienced more than 100 flank eruptions in the past 3,000 years.

^ The National Weather Service estimated the top of the ash cloud was 30,000 ft.

^ The new eruption followed a Sunday afternoon blast that sent a towering column of black ash into the clouds.

above the crater-rim, or nearly 40,000 ft. above sea-level, when it was dispersed by the wind over a very wide area. .It is believed that the amount of dust in this discharge must have been more than 2,000,000 tons.^ More than 6,000 people were killed in the earthquake.

^ More than 25,000 people have been evacuated from the surrounding area.

^ The Soufriere Hills volcano became active in 1995, and more than half the territory's 12,000 inhabitants moved away.

.Enormous quantities of dust ejected from Krakatoa in 1883 were carried to prodigious distances, samples having been collected at more than a thousand miles from the volcano; whilst the very fine material in ultramicroscopic grains which remained suspended for months in the higher regions of the atmosphere seems to have enjoyed an almost world-wide distribution, and to have been responsible for the remarkable sunsets at that period.^ Winds carried the ash to other towns in the region and across the Andes mountains to Argentina, where two airlines suspended flights due to poor visibility.

^ The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months.

^ Satellites can detect volcanoes that are more than 1500 m high because the mass of the submerged mountains causes gravity to pull the water in around them.

.The ash falling in the immediate vicinity of a volcanic vent will generally be coarser than that carried to a distance, since the particles as they are wafted through the air undergo a kind of sifting.^ Here comes that greedy helicopter pilot, offering to fly people out through the extremely heavy falling ash for $15,000 a head, in cash.
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^ Volcanic ash is falling and combining with torrential rain and high winds in the area.

^ A volcano erupted Saturday with little warning on a remote Aleutian island, sending residents of a nearby ranch fleeing from falling ash and volcanic rock.

.Professor J. W. Judd, who made an exhaustive examination of the products of the eruption of Krakatoa, found that the dust near the volcano was comparatively coarse, dense and rather darkcoloured, in consequence of the presence of numerous fragments of heavy, dark, crystalline minerals, whilst the dust at a distance was excessively fine and perfectly white.^ While I was pleasantly surprised with the amount of material I found whilst viewing Dantes Peak , it is rather Volcano that inspired this piece.
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^ It said the eruption was not likely to threaten nearby towns, but traffic near the volcano was restricted.

^ A 1993 eruption of the volcano, near the border with Ecuador, killed nine people, including five scientists who had descended into the crater to sample gases.

According to this observer, the particles tended to fall in the following order: magnetite, pyroxenes, felspar, glass. The finely comminuted material, carried to a great height in the atmosphere, consisted largely of delicate threads and attenuated plates of vitreous matter, in many cases hollow and containing air-bubbles. The greater part of the dust was formed by the mutual attrition of fragments of brittle pumice as they rose and fell in the crater, which thus became a powerful "dust-making mill." By this trituration of the pumiceous lava, carried on for a space of three months during which the eruption lasted, the quantity of finely pulverized material must have been enormous; yet the amount of ejected matter was probably very much less than that extruded during some other historical eruptions, such as that of Tomboro in Sumbawa, in 1815. The explosions at Krakatoa were, however, exceptionally violent, having been sufficient to project some of the finely pulverized lava to an altitude estimated to have been at least 30 m. .It is usually impossible during a great eruption to determine the height of the column of " smoke," since it hangs over the country as a pall of darkness.^ Clouds of white smoke are hanging over the area and continued earth tremors are keeping alive fears of another eruption.

.The great black cloud, which was so characteristic a feature in the terrible eruptions in the West Indies in 1902, was formed of steam with sulphur dioxide and other gases, very heavily charged with incandescent sand or dust, forming a dense mixture that in some respects behaved like a liquid.^ The new eruption followed a Sunday afternoon blast that sent a towering column of black ash into the clouds.

Unlike the Krakatoa dust, which was derived from a vitreous pumice, the solid matter of the black cloud was largely composed of fragments of crystalline minerals. .According to Drs Anderson and Flett it is not impossible that on the afternoon of the 17th of May 1902, the solid matter ejected from the Soufriere of St Vincent amounted to several billions of tons, and that some of the dust fell at distances more than 2000 m.^ The Soufriere Hills volcano became active in 1995, and more than half the territory's 12,000 inhabitants moved away.

^ The Soufriere Hills volcano sprang to life in 1995, chasing away more than half the British Caribbean island's population.

east of the centre of eruption.
.In Mexico and Central America, under the favourable influence of warmth and moisture, rich soils are rapidly formed by the decomposition of finely divided volcanic ejecta.^ Etna is in an almost constant state of activity, but is not considered particularly dangerous and its slopes are home to farms and vineyards that make use of the rich volcanic soil.

^ Up to 20,000 people live in the danger zone, taking advantage of the rich volcanic soil.

.Vast areas in North America, especially in Nebraska and Kansas, are covered with thick deposits of volcanic dust, partly from recent eruptions but principally from volcanic; activity in geologic time.^ The risk of a large volcanic eruption resulting from the recent Sumatra earthquakes is not great, but nevertheless should not be ignored.

^ Hiller says he was surprised to find that the density of small volcanoes dropped in the area around Iceland, as Iceland is known to be a hotspot for volcanic activity .

^ The eruptions occurred in a region where four tectonic plates, the Eurasian, Philippine, North American and Pacific, meet, causing seismic activity.

The dust is used in the arts as an abrasive agent.

Lava

.The volcanic cinders, sand, ashes and dust described above are but varied forms of solidified lava.^ "The lava is spewing hundreds of feet into the air, with the volcanic ash also 1,000 feet in the air."

Lava is indeed the most characteristic product of volcanic activity. It consists of mineral matter which is, or has been, in a molten state; but the liquidity is not due to simple dry fusion. The magma, or subterranean molten matter, may be regarded as composed essentially of various silicates, or their constituents, in a state of mutual solution, and heavily charged with certain vapours or gases, principally water-vapour, superheated and under pressure. In consequence of the peculiar constitution of the magma, the order in which minerals separate and solidify from it on cooling does not necessarily correspond with the inverse order of their relative fusibility. .The lava differs from the magma before eruption, inasmuch as water and various volatile substances may be expelled on extrusion.^ With the dam in place and reinforced by fire trucks, Jones gives the order to let the lava pool before throwing water on it.
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^ This proves the calm before the storm in more ways than one, however, as the actual eruption of a gigantic creeping flow of lava now begins.
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^ "We have indications that there may be important volumes of magma which would be liberated in an eruption," she said.

The rapid escape of vapour from the lava contributes to the explosive phenomena of an eruption, whilst the rate at which the vapour is disengaged depends largely on the viscosity of the magma.
.The lava on its immediate issue from the volcanic vent is probably at a white heat, but the temperature is difficult of determination since the molten matter is usually not easy of approach, by reason of the enshrouding vapour.^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ Although opaque white clouds float overhead in this image, skies are clear enough to allow an easy view of the volcanic plume.

.Determinations of temperature are generally made at a short distance from the exit, when the lava has undergone more or less cooling, or on a small stream from a subordinate vent.^ Clear sight lines have made it possible to gaze at Rainier and appreciate it less as an intermittent aesthetic pleasure and more for what the U.S. Geological Survey (USGS) warns that it really is.

.A. Bartoli, using a platinum electric resistance pyrometer, found that a stream of lava near a bocca, or orifice of emission, on Etna, in the eruption of 1892, had at a depth of one foot a temperature of 1060° C. In the lavas of Vesuvius and Etna thin wires of silver and of copper have frequently been melted.^ This proves the calm before the storm in more ways than one, however, as the actual eruption of a gigantic creeping flow of lava now begins.
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Probably the lava at the surface of the stream has a temperature of something like 110o° C., but this must not be assumed to be its temperature at the volcanic focus. C. Doelter, in some experiments on the melting-point of lava by means of an electric furnace, found that a lava from Etna softened at from 962° to 970° C. and became fluid at 1010° to 1040°, whilst a Vesuvian lava softened at 1030° to 1060° and acquired fluidity at 1080° to 1090°. .These results were obtained at ordinary atmospheric pressure, but it has been assumed that the melting-point of lava at a great depth would, through pressure alone, exceed that obtained in the laboratory.^ So, if the tunnel is collapsed anywhere, even partially, wouldnt that just cause the lava to break through at that point?
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.On the other hand the presence of water and of certain volatile fluxes in the magma lowers the fusing-point, and hence the extruded lava from which these have largely escaped may be much less fusible than the original magma.^ Jones has to be, conservatively, twenty years older than Heche, who also comes across as much too young (among other things) to be such a hotshot scientist.
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^ Small lahars less than a few meters wide and several centimeters deep may flow a few meters per second.

Determinations of the melting-points of various glasses formed by the fusion of certain igneous rocks have been made by J. A. Douglas, with the meldometer of Professor J. Joly. The results give temperatures ranging from 1260° C. for rhyolite to 1070° for dolerite from the Clee Hills in Shropshire. The melting-points of the rocks in a glassy condition as here given are, however, lower than those of the corresponding rocks in a crystalline state.
It should be noted that all determinations of the melting-points of minerals and rocks involving ocular inspection of the physical state of the material are liable to considerable error, and the only accurate method seems to be that of determining the point at which absorption of heat abruptly occurs - the latent heat of fusion. This has been done in the refined investigations by Mr A. L. Day and his colleagues in the Geophysical Laboratory of the, Carnegie Institution at Washington.
.It is believed that the temperature of lava in the volcanic conduit may be in some cases sufficiently high to fuse the neighbouring rocks, and so melt out a passage through them in its ascent.^ It turns out that some of the other town leaders (all men, natch) want to cover things up, in case the Evil Capitalist decides not to invest in the town.
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The wallrock thus dissolved in the magma will not be without influence on the composition of the lava with which it becomes assimilated.
.Many interesting observations are on record with regard to the heating effect of lava on metals and other objects with which it may have come in contact.^ Said reporters, by the way, are all shown directly on the other side of the wall containing the lava, and all are bereft of heat resistant clothing but are wearing jackets (!
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.Thus, after the destruction of Torre del Greco by a current of lava from Vesuvius in 1794, it was found that brass in the houses under the lava had suffered decomposition, tje copper having become crystallized; whilst silver had been not only fused but sublimed.^ Soon only the driver and NPG are left in the train as the lava flows along under the train.
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This indicates a temperature of upwards of 1000° C. Panes of glass in the windows at Torre del Greco on the same occasion suffered devitrification.
.Notwithstanding the high temperature of lava on emission, it cools so rapidly, and the consolidated lava conducts heat so slowly, that vegetable structures may be involved in a lava-flow without being entirely destroyed.^ "Centuries ago, an eruption of Gamkonora involved lava and pyroclastic flows, but in recent history, its eruptions have only been marked by spewing ash.

^ This photo captures strombolian activity and lava flows of Klyuchevskoy volcano on May 31, 2007.

.A stream of lava on entering a wood, as in the sylvan region on Etna, may burn up the undergrowth but leave many of the larger trees with their trunks merely carbonized.^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

On Vesuvius a lava-flow has been observed to surround trees while the foliage has been apparently uninjured. A vertical trunk of a coniferous tree partially enveloped in Tertiary basalt occurs at Gribon in the Isle of Mull, as described by Sir A. Geikie and others; plant-remains in basalt from the Bo'ness coalfield in Linlithgowshire have been noticed by H. M. Cadell; and attention has been called by B. Hobson to a specimen of scoriaceous basalt, from Mexico, which shows the impression of ears of maize and even relics of the actual grains. In consequence of the slow transmission of heat by solid lava, the crust on the surface of a stream may be crossed with impunity whilst the matter is still glowing at a short distance below. Lichens may indeed grow on lava which remains highly heated in the interior.
The solidified surface of a sheet of lava may be smooth and shining, sometimes quite satiny in sheen, though locally wrinkled and perhaps even ropy or hummocky, the irregularities being mainly due to superficial movement after partial solidification. The " corded lava " has a surface similar to that often seen on blastfurnace slag, and is suggestive of a tranquil flow. .After a lava stream has become crusted over on cooling, the subjacent lava, still moving in a viscous condition, tends to tear the crust, forming irregular blocks, or clinkers, which are carried forward by the flow and ultimately left in.^ Soon only the driver and NPG are left in the train as the lava flows along under the train.
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^ Heche, meanwhile, suggests dumping water on the trapped lava to form a crust, which will help in damming it up.
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the form of confused heaps, perhaps of considerable magnitude. The front of a stream may present a wall of scoriaceous fragments looking like a huge pile of coke. .As the clinkers are carried along, on the surface of the lava, they produce by mutual friction a crunching noise; and the sluggish flow of the lava-stream laden with its burden has been compared with that of a glacier.^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ He said Thursday's eruption had produced some lava flows that did not extend far from the volcano's crater.

.Since the upper part of the stream moves more rapidly than the lower, which is retarded by cooling in contact with the bed-rock, the superficial clinkers are carried forward and, rolling over the end, may become embedded in the lava as it advances.^ But while lava levels inside the crater have subsided, earth tremors have become more frequent.

^ When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter.

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

.Scoriae formed on the top of a stream may thus find their way to the base.^ He says his findings may mean that researchers need to re-assess their understanding of how submarine volcanoes are formed .

Rockfragments or other detrital matter occurring in the path of the lava will be caught up by the flow and become involved in the lower part of the molten mass; whilst the rocks over which the lava travels may suffer more or less alteration by the heat of the stream.
.The rapidity of a lava flow is determined partly by the slope of the bed over which it moves and partly by the consistency of the lava, this being dependent on its chemical composition and on the conciitions of cooling.^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ More hilly than the rest of Goma, its slopes served as a barrier to a lava flow at least two km (1.2 miles) wide.

.In an eruption of Mauna Loa, in Hawaii, in 1855, the lava was estimated to flow at a rate of 40 m.^ The eruptions forced the evacuation of thousands of villagers and damaged thousands of acres of crops buried under tons of ashes and lava flows.

^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ He said Thursday's eruption had produced some lava flows that did not extend far from the volcano's crater.

an hour; and at an eruption of Vesuvius in 1805 a velocity of more than 50 m. an hour, at the moment of emission, was recorded. The rapidity of flow is, however, rapidly checked as the stream advances, the retardation being very marked in small flows. .Where lava travels down a steep incline there is naturally a great tendency to form a rugged surface, whilst a quiet flow over a flat plane favours smoothness.^ PHIVOLCS resident volcanologist Ed Laguerta said that traces of ash deposits from lava flowing down the Mabini channel of the volcano formed small ash column that drifted to several areas south of the volcano, specifically the town of Daraga.

.If the lava meet a precipice it may form a cascade of great beauty, the clinkers rapidly rolling down with a clatter, as described by Sir W. Hamilton in the eruption of Vesuvius in 1771, when the fiery torrent had a perpendicular fall of 50 ft.^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

In Hawaii the smooth shining lava, often superficially waved and lobed, is known as pahoehoe, whilst the rugged clinker beds are termed aa. These terms are now used in general terminology, having been introduced by American geologists. The fields of aa often contain lava-balls and bombs. .It may be said that the pahoehoe corresponds practically with the Fladen lava of German vulcanologists, and the as with their Schollen lava. Rugged flows are known in Auvergne as cheires. The surface of a clinker-field has often a horribly jagged character, being covered with ragged blocks bristling with sharp points.^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

^ Subandriyo said the lava flow increased by 17 meters and reached to 100 meters.

^ The flow of lava is now said to have stopped after reaching Lake Kivu on the border.

.In the case of an obsidian-flow a most dangerous surface is produced by the keen edges and points of the fragmentary volcanic glass.^ Kelud volcanic lake is one of the most active and most dangerous stratovolcano in Indonesia.

.If, after a stream of lava has become crusted over, the underlying magma should flow away, a long cavern or tunnel may be formed.^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

Should the flow be rapid the roof may collapse and the fragments, falling on to the stream, may be carried forward or become absorbed in the fused mass. The walls and roof of a lava-cave are occasionally adorned with stalactites, whilst the floor may be covered with stalagmitic deposits of lava. The volcanic stalactites are slender, tubular bodies, extremely fragile, often knotted and rippled. Beautiful examples of lava stalactites from Hawaii have been described by Professor E. S. Dana. .Caverns may also be formed in lava-flows by the presence of large bubbles, or by the union of several bubbles.^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

^ Small lahars less than a few meters wide and several centimeters deep may flow a few meters per second.

^ PHIVOLCS resident volcanologist Ed Laguerta said that traces of ash deposits from lava flowing down the Mabini channel of the volcano formed small ash column that drifted to several areas south of the volcano, specifically the town of Daraga.

It may happen, too, that certain monticules thrown up on the surface of the lava are hollow, of which a famous example is furnished by the Caverne de Rosemond, at the base of Piton Barry, in the Isle of Reunion.
It is of great interest to determine whether molten lava contracts or expands on solidification, but the experimental evidence on this subject is rather conflicting. According to some observers a piece of solid lava thrown on to the surface of the same lava in a liquid state will sink, while according to others it floats. .It has often been observed that cakes formed by the natural fracture of the crust on the lava of Kilauea sink in the liquid mass, but it has been suggested that the fragments are drawn down by convection-currents.^ Current geological theory states that prediction is impossible (or close to it) due to the nature of sudden fracture (brittle fracture theory).

.On the other hand a solid piece, though denser than the corresponding liquid, may be buoyed up for a time by the viscous condition of the molten lava.^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

Moreover, the presence of minute vesicles may lighten the mass. .Although the minerals of a rock-magma may separately contract on crystallization it does not follow that the magma itself, in which they probably exist in a state of solution, will undergo on crystallization a similar change of volume.^ "We have indications that there may be important volumes of magma which would be liberated in an eruption," she said.

On the whole, however, there seems reason to believe that lava on solidifying almost always diminishes in volume and consequently increases in density.
Natural
Rapidly
Slowly
solid
lava.
Liquid.
cooled,
glassy.
cooled,
crystalline.
Lava of Etna
2.83
2.58-2.74
2.71-2.75
2.81-2.83
„ Vesuvius
2.83-2.85
2.68-2.74
2.6 9- 2.75
2.77-2.81
According to the experiments of C. Doelter the specific gravity of molten lava is invariably less than that of the same lava when solid, though in some cases the difference is but slight. In a vitreous or isotropic condition the lava has a lower density than when crystalline. The differences are illustrated by the following table, where the figures give the specific gravity: Experiments by Dr C. Barus showed that a diabase of specific gravity 3.017 formed a glass of sp. gr. 2.717, and melted to a liquid of sp. gr. 2.52. J. A. Douglas on examining various igneous rocks found that in all cases the rock in a vitreous state had a lower sp. gr. than in a crystalline condition, the difference being greatest in the acid plutonic rocks. A. Harker, however, has called attention to the fact that the glassy selvage of certain basic dykes in Scotland is denser than the same rock in a crystalline condition in the interior of the dykes.
Physical Structure of Lavas.-An amorphous vitreous mass may result from the rapid cooling of a lava on its extrusion from the volcanic vent. The common type of volcanic glass is known as obsidian (q.v.). Microscopic examination usually shows that even in this glass some of the molecules of the magma have assumed definite orientation, forming the incipient crystalline bodies known as microlites, &c. By the increase of these minute enclosures, in number and magnitude, the lava may become devitrified and assume a lithoidal or stony structure. If the molten magma consolidate slowly, the various silicates in solution tend to separate by crystallization as their respective points of saturation are reached. Should the process be arrested before the entire mass has crystallized, the crystals that have been developed will be embedded in the residual magma, which may, on consolidation, form a vitreous base. It is believed that in many cases the lava brings up, through its conduit, myriads of crystals that have been developed during slow solidification in the heart of the volcanic apparatus. Showers of crystals of leucite have occurred at Vesuvius, of labradorite at Etna, and of pyroxene at Vesuvius, Etna and Stromboli. These " intratelluric crystals were probably floating in the molten magma, and had they remained in suspension, this magma might on consolidation have enveloped them as a ground-mass or base. A rock so formed is generally known as a " porphyry," and the structure as porphyritic. In such a lava the large crystals, or phenocrysts, evidently represent an early phase of consolidation, and the minerals of the matrix a later stage. It is notable that the intratelluric crystals often lack sharpness of outline, as though they had suffered corrosion by attack of the molten magma, whilst they may contain vitreous enclosures, suggesting that the surrounding mass was liquid during their consolidation. It is believed that the more slowly consolidation has occurred, the larger generally are the crystals; and the higher the temperature of the magma the greater the corrosion or resorption. Possibly under certain conditions the phenocrysts and the ground-mass may have solidified simultaneously.
In some cases the entire igneous mass assumes a crystalline structure, or becomes " holocrystalline." .Such a structure is well displayed when the magma has consolidated at considerable depths, cooling slowly under great pressure, and forming rocks which are termed " plutonic " or " abyssal " to distinguish them from rocks truly volcanic, or those which, if not effusive, like lava-flows, have at least solidified very near to the surface as dykes and sills.^ The eruptions forced the evacuation of thousands of villagers and damaged thousands of acres of crops buried under tons of ashes and lava flows.

^ More hilly than the rest of Goma, its slopes served as a barrier to a lava flow at least two km (1.2 miles) wide.

Volcanic and plutonic rocks pass, however, into each other by gradual transition. The dyke-rocks, or intrusive masses, form an intermediate group sometimes distinguished under the name of " hypabyssal " rocks, as suggested by W. C. Brogger. .Lavas extruded in submarine eruptions may have solidified under a great weight of seawater, and therefore to that extent rather under plutonic conditions.^ The eruptions forced the evacuation of thousands of villagers and damaged thousands of acres of crops buried under tons of ashes and lava flows.

Chemical Composition of Lavas.-Lavas are usually classified roughly, from a chemical point of view, in broad groups according to the proportion of silica which they contain. .Those in which the proportion of silica reaches 66% or upwards are said to be acid or acidic, whilst those in which it falls to 55% or below are called basic lavas.^ Subandriyo said the lava flow increased by 17 meters and reached to 100 meters.

^ The flow of lava is now said to have stopped after reaching Lake Kivu on the border.

^ Coast Guard Petty Officer Lee Goldsmith said those at Fort Glenn reported rock and ash falling around them.

The two series are connected by a group of intermediate composition, whilst a small number of igneous rocks of exceptional type are recognized as ultrabasic. .Professor F. W. Clarke has suggested a grouping of igneous rocks as per-silicic, medio-silicic and subsilicic, in which the proportion of silica is respectively more than 60, between 50 and 60, or less than 50%.^ When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter.

^ Small lahars less than a few meters wide and several centimeters deep may flow a few meters per second.

^ By eroding rock debris and incorporating additional water, lahars can easily grow to more than 10 times their initial size.

I.
II.
III.
IV.
V.
VI.
Silica
48.28
49.73
50.00
68.99
61 88
49.20
Alumina
18.39
18.4 6
1 3.99
16.07
18.30
14.90
Ferric oxide
I 12
6.95
5.1 3
2.6 3
1 97
4.51
Ferrous oxide .
7.88
5.59
9.10
1 IO
4.32
12.75
Manganous oxide .
..
..
..
0.28
..
0.28
Magnesia.. .
3.7 2
3.99
4.06
i 08
2.71
3.90
Lime. .
9.20
10.71
io. 81
3.16
6.32
9.20
Soda.. .
2.84
. 50
. 02
4.04
. 17
1.96
Potash
7.25
1.07
2.87
1.83
1.09
0.95
Titanium dioxide
1.28
..
..
0.82
0.31
1.72
Phosphorus pentoxide
0.51
..
0.09
0.42
Loss on ignition
0.62
..
0.24
..
0.19
o Io
100 96
100.00
99.22
100 00
100.35
99.89
By far the greater part of all lavas consists of various silicates, either crystallized as definite minerals or unindividualized as volcanic glass. In addition, however, to the mineral silicates, a volcanic rock may contain a limited amount of free acid and basic oxides, represented by such minerals as quartz and magnetite. Rhyolite may be cited as a typical example of an acid lava, andesite as an intermediate and basalt as a basic lava. The various volcanic rocks are described under their respective headings, so that it is needless to refer here to their chemical or mineralogical composition. .It may, however, be useful to cite a few selected analyses of some recent lavas and ashes: I. From Vesuvius, eruption of 1906; by M. Pisani.^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ The eruptions forced the evacuation of thousands of villagers and damaged thousands of acres of crops buried under tons of ashes and lava flows.

^ A brief eruption in May of 1994 sent ash to 10.5 km.

II. Etna. Mean of several analyses by Silvestri and Fuchs (Mercalli).
III. „ Stromboli, 1891; by Ricciardi.
IV. „ Krakatoa, eruption of 1883; by C. Winkler.
V. „ Mont Pele, Martinique, eruption of 1902; by M. Pisani.
VI. „ Kilauea, Hawaii; by O. Silvestri.
.In the course of the life of a volcano, the lava which it emits may undergo changes, within moderate limits, being at one time more acid, at another more basic.^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ Raging lava has spewed out of one of the world's most active volcanos on the French island of La Reunion.

^ Lava has oozed from a new location on Kilauea, one of the worlds most active volcanoes, scientists said.

Such changes are sometimes connected with a shifting of the axis of eruption. Thus at Etna the lavas from the old axis of Trifoglietto in the Valle del Bove were andesites, with about 55% of silica, but those rising in the present conduit are doleritic, with a silica-content of only about 50%. It seems probable that, to a limited extent, changes in the character of a lava may sometimes be due to contact of the magma with different rocks underground: if these are rich in silica, the acidity of the lava will naturally increase; while if they are rich in calcareous and ferromagnesian constituents, the basicity will increase: the variation is consequently apt to be only local, and probably always slight.
.By von Richthofen and some others it has been held that during a long period of igneous activity a definite order in the succession of the erupted rocks is everywhere constant; but though some striking coincidences may be cited, it can hardly be said that this generalization has been satisfactorily established.^ LLaima's renewed activity comes after Chaiten volcano, 760 miles (1,220 km) south of Santiago in Chilean Patagonia, erupted on May 2 for the first time in thousands of years, spewing ash, gas and molten rock.

^ Kim said people living in older and established communities often prefer to stay with friends or family during evacuations.

^ By nightfall, at least 1,100 were back in camps and some 12,000 others were given orders to leave.

It has, however, often been observed, as emphasized by Professor Iddings, that a volcanic centre will start with the emission of lavas of neutral or intermediate type, followed in the course of a geological period by acid and basic lavas, and ending with those of extreme composition, indicating progressive change in the magma.
The old idea of a universal magma, or continuous pyrosphere, has been generally abandoned. Whatever may have been the case in a primitive condition of the interior of the earth, it seems necessary to admit that the magma must now exist in separate reservoirs. .The independent activity of neighbouring volcanoes strikingly illustrated in Kilauea and Mauna Loa in Hawaii, only 20 m.^ The voluntary evacuation advisory covered the Mauna Loa Estates, Ohia Estates and Volcano Golf Course subdivisions as well as the Volcano Village and Keauhou Ranch areas.

^ Mauna Loa, Hawaii (Active!

apart, suggests a want of communication between the conduits; and though the lavas are very similar at these two centres, it would seem that they can hardly be drawn from a common source. .Again, the volcanoes of southern Italy and the neighbouring islands exhibit little or no sympathy in their action, and emit lavas of diverse type.^ A volcano erupted Saturday with little warning on a remote Aleutian island, sending residents of a nearby ranch fleeing from falling ash and volcanic rock.

The lavas of Vulcano, one of the Lipari Isles, are rhyolitic, whilst those of Stromboli, another of the group, are basaltic.
It is believed that the magma in a subterranean reservoir, though originally homogeneous, may slowly undergo certain changes, whereby the more basic constituents migrate to one quarter whilst the acid segregate in another, so that the canal, at successive periods, may bring up material of different types. The cause of this " magmatic differentiation," which has been the subject of much discussion, is of fundamental importance in any broad study of the genetic relations of igneous rocks.
It has often been observed that all the rocks from a definite igneous centre have a general similarity in chemical and mineralogical characters. This relationship is called, after Professor Iddings, " consanguinity," and appears to be due to the fact that the rocks are drawn from a common source. Professor Judd pointed out the existence of distinct " petrographical provinces," within which the eruptive rocks during a given geological period have a certain family likeness and have appeared in definite succession. Thus he recognized a Brito-Icelandic petrographical province of Tertiary and recent lavas. It has been shown by A. Harker that alkali igneous rocks are generally associated with the Atlantic type of coast-line and sub-alkali rocks with the Pacific type.
.Although changes in the character of an erupted product from a given centre are usually brought about very slowly, it has often been supposed that even in the course of a single prolonged eruption, or series of eruptions, the character of the lava may vary to some extent.^ These dynamics are the very reason science has been puzzled about the change in time prediction model regarding Parkfield.

^ He said Thursday's eruption had produced some lava flows that did not extend far from the volcano's crater.

That this is not, however, usually the case has been repeatedly proved. .M. H. Arsandaux, for instance, analysed the bombs of augite-andesite thrown out from Santorin at the beginning of the eruption of 1866, others ejected in 1867, and others again at the close of the eruption in 1868; and he found no important variation in the composition of the magma during these successive stages.^ "We have indications that there may be important volumes of magma which would be liberated in an eruption," she said.

Moreover, Professor A. Lacroix found that the material extruded from Vesuvius in 1906 remained practically of the same composition from the beginning to the end of the eruption, and further, that it presented great analogy to that of 1872 and even to that of 1631.
All the Vesuvian lavas are of the type of rock known as leucotephrite or leucitetephrite, or they pass, by the presence of a little olivine, into leucite-basanite. Leucite is characteristic of the lavas of Vesuvius, whilst it is excessively rare in those of Etna, where a normal doleritic type prevails. Nepheline, a felspathoid related to leucite, is characteristic of certain lavas, such as those of the Canary Islands, which comprise nepheline-tephrites and nepheline-basanites. .Most of the lavas from the volcanoes of South America consist of hypersthene-andesite, and it is notable that the fragmental ejectamenta from the eruptions of St Vincent and Martinique in 1902 and from Krakatoa in 1883 were evidently derived from a magma of this Pacific type.^ The volcano spread ashes for kilometers prompting an evacuation order for thousands, in the most serious eruption of the Galeras since its reactivation in 1989.

^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ Raging lava has spewed out of one of the world's most active volcanos on the French island of La Reunion.

It commonly happens that acid lavas are paler in colour, less dense and less fusible than basic lavas, and they are probably drawn in some cases from shallower depths. .As a consequence of the ready fusibility of many basic lavas, they flow freely on emission, running to great distances and forming far-spreading sheets, whilst the more acid lavas rapidly become viscid and tend to consolidate nearer to their origin, often in hummocky masses.^ He said Thursday's eruption had produced some lava flows that did not extend far from the volcano's crater.

^ Authorities ordered 116,000 people living along the fertile slopes to evacuate, but many have refused, saying they need to tend to their crops and animals.

^ But while lava levels inside the crater have subsided, earth tremors have become more frequent.

.The shape of a volcanic mountain is consequently determined to a large extent by the chemical character of the lavas which it emits.^ It is popular with mountaineers and is seen as having one of the world's most perfect volcanic cone shapes.

In the Hawaiian Islands, for instance, where the lavas are highly basic and fluent, they form mountains which, though lofty, are flat domes with very gently sloping sides. .Such is the fluidity of the lava on emission that it flows freely on a slope of less than one degree.^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

^ Small lahars less than a few meters wide and several centimeters deep may flow a few meters per second.

^ More hilly than the rest of Goma, its slopes served as a barrier to a lava flow at least two km (1.2 miles) wide.

.In consequence, too, of this mobility, it is readily thrown into spray and even projected by the expansive force of vapour into jets, which may rise to the height of hundreds of feet and fall back still incandescent, producing the appearance of "fire fountains."^ The Volcano of Fire, rising some 12,664 feet into the sky, has been relatively active since 1998 but saw activity increase dramatically in the past week, causing about 120 small earthquakes a day.

^ Hundreds of thousands of people in the Goma area - a part of the country controlled by rebel forces - were forced to flee into Rwanda to escape the lava flow.

^ "The lava is spewing hundreds of feet into the air, with the volcanic ash also 1,000 feet in the air."

.The emission is not usually accompanied, however, by violent explosions, such as are often associated with the eruption of magmas of less basic and more viscous nature.^ The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months.

.The viscosity of the lava at Kilauea was estimated by G. F. Becker to be about fifty times as great as that of water.^ The volcano is about 530,000 years old and has erupted an estimated 170 times since the mid 17th century.

It may be pointed out that the fusibility of a lava depends not on the mere fact that it is basic, but rather on the character of the bases. A lava from Etna or Vesuvius may be really as basic as one from Hawaii.

Capillary Lava

.A filamentous form of lava well known at Kilauea, in Hawaii, is termed Pele's hair, after Pele, the reputed goddess of the Hawaiian volcanoes.^ Lava has oozed from a new location on Kilauea, one of the worlds most active volcanoes, scientists said.

^ Volcanologists said the volcano appeared to be destroying a small lava dome which had formed in the crater since mid-November.

It resembles the capillary slag much used in the arts under the name of " mineral wool " - a material formed by injecting steam into molten slag from an iron blast-furnace. .It is commonly supposed that Pele's hair has been formed from drops of lava splashed into the air and drawn out by the wind into fine threads.^ "The lava is spewing hundreds of feet into the air, with the volcanic ash also 1,000 feet in the air."

According, however, to Major C. E. Dutton, the filaments are formed on the eddying surface of the lava by the elongation of minute vesicles of water-vapour expelled from the magma. C. F. W. Krukenberg, who examined the hair microscopically, figured a large number of fibres, some of which showed the presence of minute vesicles and microscopic crystals, the former when drawn out rendering the thread tubular. In a spongy vitreous scoria from Hawaii, described as " thread-lace," a polygonal network of delicate fibres forms little skeleton cells. .Capillary lava is not confined to the Hawaiian volcanoes: it is known, for example, in Reunion, and may be formed even at Vesuvius.^ He says his findings may mean that researchers need to re-assess their understanding of how submarine volcanoes are formed .

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ Raging lava has spewed out of one of the world's most active volcanos on the French island of La Reunion.

Pumiceous Lava. - The copious disengagement of vapour in a glassy lava gives rise to the light cellular or spongy substance, full of microscopic pores, known as pumice (q.v.). It is usually, though not invariably, produced from an acid lava, and may sometimes be regarded as the solidified foam of an obsidian. .During the eruption of Krakatoa in 1883 enormous quantities of pumice were ejected, and were carried by the sea to vast distances, until they ultimately became water-logged and sank.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

.Professor Judd found the pumice to consist of a vitreous lava greatly inflated by imprisoned vapours; the walls of the air-cells were formed of the lava drawn out into thin plates and threads, often with delicate fibres running across the cavities.^ "The lava is spewing hundreds of feet into the air, with the volcanic ash also 1,000 feet in the air."

Having been suddenly cooled, it was extremely brittle, and its ready pulverization gave rise to much of the ash ejected during this eruption. It has been shown by Dr JohnstonLavis that a bed of pumiceous lava, especially if basic, is generally vitreous towards the base, becoming denser, darker and more crystalline upwards, until it may pass superficially into scoria. The change is explicable by reduction in the temperature of the magma consequent on the conversion of water into steam.
Water in Lavas. - Whether an eruption is of an explosive or a tranquil character must depend largely, though not wholly, on the chemical composition of the magma, especially on the extent to which it is aquiferous. By relief of pressure on the rise of the column in the volcanic channel, or otherwise, more or less steam will be disengaged, and if in large quantity this must become, with other vapours, a projectile agency of enormous power. The precise physical condition in which water exists in the magma is a matter of speculation, and hence Johnston-Lavis proposed to designate it simply as H 2 O. Water above its critical point, which is about 370° C. or 698°F., cannot exist as a liquid, whatever be the pressure, neither is it an ordinary vapour. It has been estimated that the critical point would probably be reached at a depth of about 7 m. At very high temperatures the elements of water may exist in a state of dissociation.
Much discussion has arisen as to the origin of the volcanic water, but probably it is not all attributable to a single source. Some may be of superficial origin, derived from rain, river or sea; whilst the upward passage of lava through moist strata must generate large volumes of steam. .It has often been remarked that wet weather increases the activity of a volcano, and that in certain mountains the eruptions are more frequent in winter.^ Satellites can detect volcanoes that are more than 1500 m high because the mass of the submerged mountains causes gravity to pull the water in around them.

^ Liliana Troncoso of Ecuador 's Geophysics Institute told The Associated Press that Reventador volcano had been showing increasing signs of activity since January, but that this eruption does not pose a threat to any nearby villages.

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

.According, however, to Professor A. Ricco's prolonged study of Etna, rain has no apparent influence on the activity of this mountain, and indeed the number of eruptions in winter, when rains are abundant, seems rather less than in summer.^ No eruption has occurred yet, but seismic activity has commenced.

.The popular belief that explosive action is due to the admission of water to the volcanic focus is founded mainly on the topographic relation of volcanoes to large natural bodies of water, many being situated near the shore of a continent or on islands or even on the sea-floor.^ Volcano erupts on Red Sea island A search for survivors is under way after a volcano erupted on a Yemeni island in the Red Sea, killing at least two people.

^ The current lake volume is large enough that it will influence the next phase of eruptive activity from the volcano and result in a new hazard to people visiting the island.

^ Large earthquakes are capable of disturbing volcanic systems, and a watch should be kept over the volcanoes of Sumatra and Andaman Islands for change in activity.

Salt water gaining access to heated rocks, through fissures or by capillary absorption, would give rise not only to watervapour but to the volatile chlorides so common in volcanic exhalations. .Yet it is notable that comparatively little chlorine is found among the products exhaled by the volcanoes of Hawaii, though these are typically insular.^ Another surprise was that he found fewer volcanoes on the seabed around Hawaii, another volcanic hotspot.

.L. Palmieri, however, described certain sublimates on lava at Vesuvius after the eruption of 1872 as deposits of " sea-salt," to show that they were not simply sodium chloride, but contained other constituents found in sea-water.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

.Professor T. J. J. See believes that sea-water gains access to the heated rocks of the earth's interior by leakage through the floor of the ocean, the bottom never being water-tight, and Arrhenius supposes that it reaches the magma by capillarity through this floor.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

^ The survey crew also found grayish mud rising up from the bottom of the ocean, but it was not immediately known whether any volcanic gases are being released.

^ "But the problem is that we cannot see through the water to count them," he says.

.It has been supposed that water on reaching the hot walls of a subterranean cavity would pass into the spheroidal state, and on subsequent reduction of temperature might come into direct contact with the heated surface, when it would flash with explosive violence into steam.^ The red hot lava cut roads in half, damaged homes and created huge clouds of steam as it flowed into the Indian Ocean.

Such catastrophes probably occur in certain cases. .When, for example, a volcano becomes dormant, water commonly accumulates in the crater, and on a renewal of activity this craterlake may be absorbed through fissures in the floor leading to the reopened duct, and thus become rapidly, even suddenly, converted into vapour.^ LLaima's renewed activity comes after Chaiten volcano, 760 miles (1,220 km) south of Santiago in Chilean Patagonia, erupted on May 2 for the first time in thousands of years, spewing ash, gas and molten rock.

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

.But such incidents are accidental rather than normal, and seem incompetent to account for volcanic activity in general.^ Volcanic activity generates harmonic scalar resonance precursors.

The effect of the contact of lava with water is often misunderstood.
.When a stream of lava flows into the sea it no doubt immediately generates a prodigious volume of steam; but this is only a temporary phenomenon, for the lava rapidly becomes chilled by the cold water, with formation of a superficial solid layer, which by its low thermal conductivity allows the internal mass to cool slowly and quietly.^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ There have been no lava flows since the volcano began spitting out ash in December, he said.

.In the great eruption of Krakatoa in 1883 the sea-water gained occasional access to the molten lava, and by its cooling effect checked the escape of vapour, thus temporarily diminishing the volcanic activity.^ The risk of a large volcanic eruption resulting from the recent Sumatra earthquakes is not great, but nevertheless should not be ignored.

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

But Judd compares this action to that of fastening down the safety-valve of a steam-boiler. The tension of the elastic fluids being increased by this repression would give rise subsequently to an explosion of greater violence; and hence the short violent paroxysms characteristic of the Krakatoa eruption were due to what he calls a " check and rally " of the subterranean forces. The action in the volcanic conduit has, indeed, been compared with that of a geyser.
.The downward passage of water through fissures must be confined to the upper portion of the earth's crust known as the " zone of fracture," for it is there only that open channels can exist.^ With proper filters and a scalar resonant receiver, the earth signals & activity opens up the crust as an MRI machine opens up the view of the body.

^ There are fissures opening up in the town which billow smoke.

Water might also percolate through the pores of the rocks, but even the pores are closed at great depths. .It was shown many years ago by G. A. Daubree that water could pass to a limited extent through a heated rock against the pressure of steam in the opposite direction.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

.According to S. Arrhenius, water may pass inwards through the sea-bottom by osmotic pressure.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

As the melting points of various silicates are lowered by admixture with water, it appears that the access of surface-waters to heated rocks must promote their fusibility. Judd has suggested that the proximity of large bodies of water may be favourable to volcanic manifestations, because the hydrated rocks become readily melted by internal heat and thus yield a supply of lava.
.Whilst some of the water-vapour exhaled from a volcano is undoubtedly derived from superficial sources, notably in such insular volcanoes as Stromboli, the opinion has of late years been gaining ground, through the teaching of Professor E. Suess and others, that the volcanic water must be largely referred to a deep-seated subterranean origin - that it is, in a word, " hypogene " or magmatic rather than meteoric.^ Satellites can detect volcanoes that are more than 1500 m high because the mass of the submerged mountains causes gravity to pull the water in around them.

^ Lake Toba is a large caldera formed by volcanic and tectonic processes, and was the site of the world's most recent supervolcano 74,000 years ago.

^ The most important step science needs to take is to open up the paradigm model rather than continue to detract sources of insight.

.It is held that the magma as it rises through the volcanic conduit brings up much water-vapour and other gaseous matters derived from original sources, perhaps a relic of what was present in the earth in its molten condition, having possibly been absorbed from a dense primordial atmosphere, or, as suggested by Professor T. C. Chamberlin, entrapped by the globe during its formation by accretion of planetesimal matter.^ Volcanic ash moves quickly through the atmosphere, so it's important for scientists to have up-to-date information at their f Twice a day, the GI/AVO am goes through a rigorous process to examine the current condition of the more than 150 active volcanoes in the North Pacific.

^ The seismic network recorded about 394 tremor episodes and four volcanic quakes during the past 24 hours signifying magma activity in the volcano.

^ The survey crew also found grayish mud rising up from the bottom of the ocean, but it was not immediately known whether any volcanic gases are being released.

.Water brought from magmatic depths to the surface, and appearing there for the first time, has been termed " juvenile," and it has been assumed that such water may be seen in hot springs like those at Carlsbad.^ Chaitn first came to Chiles and the worlds attention on May 1, 2008 when it erupted for the first time in recorded history.

Professor J. W. Gregory has suggested that certain springs in the interior of Australia may derive part of their supply from juvenile or plutonic waters.
According to A. Gautier, the origin of volcanic water may be found in the oxidation of hydrogen, developed from masses of crystalline rock, which by subsidence have been subjected to the action of subterranean heat.

Volcanic Vapours

It seems not unlikely that the vapours and gases exist in the volcanic magma in much the same way that they can exist in molten metal. It is a familiar fact that certain metals when melted can absorb large volumes of gases without entering into chemical combination with them. .Molten silver, for example, is capable of absorbing from the atmosphere more than twenty times its volume.^ This is over 10 times more than have been found before.

^ By eroding rock debris and incorporating additional water, lahars can easily grow to more than 10 times their initial size.

^ (March 10) - A volcano in southern Japan erupted Tuesday, sending cinders more than a mile from the crater, The Straits Times reports .

of oxygen, which it expels on solidification, thus producing what is called the " spitting of silver." Platinum again can absorb and retain when solid, or occlude, a large volume of hydrogen, that can be expelled by heating the metal in vacuo. In like manner molten rock under pressure can absorb much steam. It appears that many igneous rocks contain gases locked up in their pores, not set free by pulverization, yet capable of expulsion by strong heat. The gases in rocks have been the subject of elaborate study by R. T. Chamberlin, whose results appear in Publication No. 106 of the Carnegie Institution of Washington.
Sir W. A. Tilden has found that granite, gabbro, basalt and certain other igneous rocks enclose many times their volume of gases, chiefly hydrogen and carbon dioxide, with carbon monoxide, methane and nitrogen. Thus, the basalt of Antrim in Ireland, which is a Tertiary lava, yielded eight times its volume of gas having the following percentage composition: hydrogen 36.15, carbon dioxide 32.08, carbon monoxide 20.08, methane 10, nitrogen 1.61. No doubt some of the gases evolved on heating rocks may be generated by reactions during the experiment, as shown by M. W. Travers, and also by Armand Gautier. .It has been pointed out by Gautier that the gas exhaled from Mont Pele during the eruption of 1902 had practically the same composition as that which he obtained on heating granite and certain other rocks.^ As compared to the eruption of 1956, the only one in the history of modern observations, the current eruption started in a more impetuous and powerful way the scientist pointed out.

According to this authority a cubic kilometre of granite heated to redness would yield not less than 26,000,000 tons of water-vapour, besides other gases. If then a mass of granite in the earth's crust were subject to a great local accession of heat it might evolve vast volumes of gaseous, matter, capable of producing an eruption of explosive type. Judd found that the little balls of Siberian obsidian called marekanite threw off, when strongly heated, clouds of finely divided particles formed by rupture of the distended mass through the escape of vapour. Pitchstone when ignited loses in some cases as much as to % of its weight, due to expulsion of water.
.Much of the steam and other vapour brought up from below by the lava may be evolved on mere exposure to the air, and hence a stream freshly extruded is generally beclouded with more or less vapour.^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

Gaseous bubbles in the body of the lava render it vesicular,. especially in the upper part of a stream, where the pressure is relieved, and the vesicles by the onward flow of the lava tend to become elongated in the direction of movement. Vesiculation, being naturally resisted by cohesion, is not common in very viscid lavas of acid type, nor is it to be expected where the lava has been subject to great pressure, but it is seen to perfection in surface-flows of liquid lavas of basaltic character. A vesicular structure may sometimes be seen even in dykes, but the cavities are usually rounded rather than elongated, and are often arranged in bands parallel to the walls of the dyke. A very small proportion of water in a lava. suffices to produce vesiculation. Secondary minerals developed in a cellular lava may be deposited in the steam-holes, thus producing an amygdaloidal rock.
After the surface of a lava-stream has become crusted over, vapour may still be evolved in the interior of the mass, and in seeking release may elevate or even pierce the crust. .Small cones may thus be thrown up on a lava-flow, and when vapour escapes from terminal or lateral orifices they are known as " spiracles."^ Hundreds of thousands of people in the Goma area - a part of the country controlled by rebel forces - were forced to flee into Rwanda to escape the lava flow.

^ They were later picked up by a vessel responding to a Coast Guard request for emergency assistance.

^ This photo captures strombolian activity and lava flows of Klyuchevskoy volcano on May 31, 2007.

The steam may issue with sufficient projectile force to toss up the lava in little fountains. .When the lava is very liquid, as in the Hawaiian volcanoes, it may after projection from the blow-hole fall back in drops and plastic clots, which on consolidation form, by their union, small cones.^ He says his findings may mean that researchers need to re-assess their understanding of how submarine volcanoes are formed .

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ PHIVOLCS resident volcanologist Ed Laguerta said that traces of ash deposits from lava flowing down the Mabini channel of the volcano formed small ash column that drifted to several areas south of the volcano, specifically the town of Daraga.

Vapour-vents on lava are often known as fumaroles (q.v.). The character of the gaseous exhalations varies with the temperature, and the following classification was suggested by C. Sainte-Claire Deville: (1) Dry or white fumaroles having a temperature above 500° C. and evolving compounds of chlorine, and perhaps fluorine. (2) Acid fumaroles, exhaling much steam, with hydrocholoric acid and sulphur dioxide. (3) Alkaline fumaroles, at a temperature of about 100°, with much steam and ammonium chloride and some sulphuretted hydrogen. (4) Cold fumaroles, below100°, with aqueous vapour, carbon dioxide and sulphuretted hydrogen. (5) Mofettes, indicating the expiring phase of vulcanism. A similar sequence of emanations, following progressive cooling of the lava, has been noted by other observers. During an eruption, the gaseous products may vary considerably. Johnston-Lavis found at Vesuvius that the vapour which first escaped from the boiling lava contained much sulphurous acid, and that hydrochloric acid and other chlorides. appeared later.
.If the vapours exhaled from volcanoes were derived originally from superficial sources, the lava would, of course, merely return to the surface of the earth what it had directly or indirectly absorbed.^ ORIGINAL CAPTION : Superheated ash and lava is visible inside the cone of the Soufriere Hills volcano, which has been active lately, as seen from Olveston, Montserrat, on Jan.

.But if, as is now rather generally believed, much if not most of the volcanic vapour is derived from original subterranean sources, it must form a direct contribution from the interior of the earth to the atmosphere and hydrosphere, and consequently becomes of extreme geological interest.^ Lake Toba is a large caldera formed by volcanic and tectonic processes, and was the site of the world's most recent supervolcano 74,000 years ago.

Description of Special Gases and Vapours. - Hydrochloric acid, HCI, escapes abundantly from many vents, often accompanied with the vapours of certain metallic chlorides, and is responsible for much of the acrid effects of volcanic exhalations. To avoid dangerous vapours an active volcano should be ascended on the windward side. Free hydrofluoric acid, HF, has sometimes been detected with the hydrochloric acid among Vesuvian vapours, and silicon fluoride, SiF 4, has also been reported. Sulphuretted hydrogen, H 2 S, is a frequent emanation, and being combustible may contribute to the lambent flames seen in some eruptions. It readily suffers oxidation, giving rise to sulphur dioxide and water. By the interaction of hydrogen sulphide and carbon dioxide, water and carbon oxysulphide, COS, are formed; whilst by reaction with sulphur dioxide, water and free sulphur are produced, such being no doubt the origin of many deposits of volcanic sulphur. Hydrogen sulphide may be formed by the decomposition of certain metallic sulphides, like that of calcium, in the presence of moisture, as suggested by Anderson and Flett with regard to certain muds at the Soufriere of St Vincent. Sulphur dioxide, S02, is one of the commonest exhalations, especially at acid fumaroles. It may be detected by its characteristic smell, that of burning brimstone, even when present in very small proportion and in the presence of an excess of hydrochloric acid. By hydration it readily forms sulphurous acid, which may be further oxidized to sulphuric acid. .J. B. Boussingault found free sulphuric acid (with hydrochloric acid) in the water of the Rio Vinagre which issues from the volcano of Purace in the Andes of Colombia; and it occurs also in certain other volcanic waters.^ The volcano still poses a hazard to the local population with ashfall and acid rain affecting food crops and drinking water.

Carbon dioxide, C02, is generally a product of the later stages of an eruption and is often evolved after all other gases have ceased to escape. Although it may sometimes be due to the decomposition of limestone, it seems to be mostly of true magmatic origin. At the well-known Grotta del Cane, at Lake Agnano, in the Phlegraean Fields near Naples, there has been for ages a copious discharge, and analyses of the air of the cave by T. Graham Young showed the presence of from 61.5 to 7 1% of carbon dioxide. Gautier, in 1907, found 96 to 97% of this gas in the vapours (excluding water-vapour) emitted from the Solfatara near Pozzuoli in the Bay of Naples. The gas by its density tends to accumulate in depressed areas, as in the Death Gulch in the Yellowstone Park and in the Upas Valley of Java. In the Eifel, in the Auvergne and in many other volcanic regions it is discharged at temperatures not above that of the atmosphere. This natural carbonic acid gas is now utilized industrially at many localities. In the gases of the fumaroles of Mont Pele, carbon monoxide, CO, was detected by H. Moissan. Probably certain hydrocarbons, notably methane or marsh-gas, CH4, often exist in volcanic gases. They might be formed by the action of water on natural carbides, such as that of magnesium, calcium, &c. Moissan found 5.46% of methane in vapour from a fumarole on Mont Pele in 1902. Free hydrogen was detected by R. Bunsen as far back as 1846 in vapours from volcanoes in Iceland. In 1861 Deville and Fouque found it, with hydrocarbons, at Torre del Greco near Naples; and in 1866 Fouque discovered it at Santorin, where some of the vapour at the immediate focus of eruption contained as much as 30% of hydrogen. It is notable that at Santorin free oxygen was also found. .The elements of water may possibly exist, at the high temperature of the magma, in a state of dissociation, and certain volcanic explosions have sometimes been attributed to the combination of these elements.^ These clues suggest that the material underlying Yellowstone is still very hot and ductile, as would be expected if a magma chamber still exists.

Oxygen is not infrequently found among volcanic emanations, but may perhaps be derived in most cases from superficial air and ground-water; and in like manner the nitrogen, often detected, may be sometimes of atmospheric origin, though in other cases derived from nitrides in the lava. In the vapours emitted by Mont Pele in 1902 argon was detected by H. Moissan, to the extent of 0.71%; and in those from Vesuvius in 1906 argon and neon were found by Gautier. The collection of volcanic vapours offers difficulty, and it is not easy to avoid admixture with the atmosphere. F. A. Perret has successfully collected gases on,Vesuvius.
Volcanic Flames. - .Although the incandescence of the lava and stones projected during an eruption, and the reflection from incandescent matter in the crater have often been mistaken for red flames, there can be no doubt that true combustion, though generally feeble, does occur during volcanic outbursts.^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

^ There have been no deaths associated with the eruptions that began earlier this month, but thousands of villagers have been evacuated from the area.

^ There have been no lava flows since the volcano began spitting out ash in December, he said.

Among the gases cited above, hydrogen, hydrogen sulphide and the hydrocarbons are inflammable. The flames seen in volcanoes are generally pale and of bluish, greenish or yellowish tint. They were first examined spectroscopically by J. Janssen, who in 1867 detected the lines of burning hydrogen at Santorin. Subsequently he proved the presence of hydrogen, sodium and hydrocarbons in the volcanic flames of Kilauea. .During the eruption of Vulcano, in the Lipari Isles, in 1888, flames with a bluish or greenish tinge were seen by A. E. Narlian, an experienced observer resident in the island. These, however, were referred to the kindling of sulphur deposited around the fumaroles, the flames being coloured by the presence of boric acid and arsenic sulphide.^ While a small number of soldiers were stationed on the island, one was killed during an eruption in June of 1944.

When a stream of lava flows over vegetation the combustion of the leaves and wood ma y be mistaken for flames issuing from the lava. .In like manner brushwood may grow in the crater of a dormant volcano and be ignited by a fresh outburst of lava, thus producing flames which, from their position in the crater, may readily deceive an observer.^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ He said Thursday's eruption had produced some lava flows that did not extend far from the volcano's crater.

Volcanic Sublimates

Certain mineral substances occur as sublimates in and around the volcanic vents, forming incrustations on the lava. They are either deposited directly from the effluent vapours, which carry them in a volatile condition, or are produced by interaction of the vapours among themselves; whilst some of the incrustations, rather loosely called sublimates, are due to reaction of the vapours on the constituents of the lava. Possibly at the temperature of the magma-reservoirs even silica and various silicates may be volatilized, and might thus yield sublimation products. Many of the volcanic sublimates occur at first as incandescent crusts on the lava. Being generally unstable they are difficult of preservation, and are not usually well represented in collections.
Among the commonest sublimates is halite, or sodium chloride, NaCI, occurring as a white crystalline incrustation, sometimes accompanied, as at Vesuvius, by sylvite, or potassium chloride, KC1, which forms a similar sublimate. The two chlorides may be intimately associated. Sal ammoniac, or ammonium chloride, NH 4 C1, is not uncommon, especially at Etna, as a white crystalline crust, probably formed in part by the reaction of hydrochloric acid with nitrogen and hydrogen in the vapours. Bunsen, on finding it in Iceland, regarded it as a product of the distillation of organic matter. At the Solfatara, near Pozzuoli, sal ammoniac was formerly collected as a sublimate on tiles placed round a bocca or vapourvent. Ferric chloride, FeCl 3, not infrequently occurs as a reddish or brownish yellow deliquescent incrustation, and because it thus colours the lava it has received the name of molysite (from Gr.
µ6Xvvns, stain). The action of hydrochloric acid on the iron compounds in the lava may readily yield this chloride, which from its yellowish colour has sometimes been mistaken for sulphur. A crystalline sublimate from the fumaroles on Vesuvius, containing ferric and alkaline chlorides, KCl NH 4 Cl 2FeC1 3 +6H 2 O, is known as kremersite, after P. Kremers. From a scoriaceous lava found on Vesuvius after the eruption of 1906, Johnston-Lavis procured a yellow rhombohedral sublimate, which he proved to be a chloride of manganese and potassium, whence he proposed for it the name chlormanganokalite. It was studied by L. J. Spencer, and found to contain 4KC1. MnC1 2. Chlorocalcite, or native calcium chloride, CaC1 2, has been found in cubic crystals on Vesuvian lava. Fluorite, or calcium fluoride, CaF 2, is also known as a volcanic product. Lead chloride, PbC1 2, a rare Vesuvian mineral, was named cotunnite, after Dr Cotugno of Naples. The action of hydrogen sulphide on this chloride may give rise to galena, PbS, found by A. Lacroix on Vesuvius in 1906. Atacamite, or cupric oxychloride, CuC1 2.3Cu (OH)2, occurs as a green incrustation on certain Vesuvian lavas, notably those of 1631. Another green mineral from Vesuvius was found by A. Scacchi to be a sulphate containing copper, with potassium and sodium, which he named from its fine colour euclorina - a word which has been written in English as euchlorinite. The copper in the sublimates on Vesuvius will sometimes plate the iron nails of a traveller's boots when crossing the newly erupted lava. Cupric oxide, CuO, occurs in delicate crystalline scales termed tenorite, after Professor G. Tenore of Naples; whilst cupric sulphide, CuS, forms a delicately reticulated incrustation known as covellite, after N. Covelli, its discoverer at Vesuvius.
A sublimate not infrequently found in feathery crystalline deposits on lava at Vesuvius, and formerly called " Vesuvian salt," is a potassium and sodium sulphate, (K. Na) 2 SO 4, known as aphthitalite (from Gr. a4B%Tos, imperishable, and &As, salt). A sulphate with the composition PbS04 (K Na)2S04, found in the fumaroles at Vesuvius after the eruption of 1906, was named by A. Lacroix palmierite, after L. Palmieri, who was formerly director of the observatory on Vesuvius. Various sulphites are formed on lavas by the sulphurous acid of the vapours. Ferric oxide, Fe203, which occurs in beautiful metallic scales as specular iron-ore, or as an amorphous reddish incrustation on the lava, is probably formed in most cases by the interaction of vapour of ferric chloride and steam at a high temperature. Less frequently, magnetite, Fe304, and magnesioferrite, MgFe204, are found in octahedral crystals on lava. An iron nitride (Fe5N2) was detected thinly incrusting a lava erupted at Etna in 1874, and was named by 0. Silvestri, who examined it, siderazote.
Boric acid, H3B03, occurs in the crater of Vulcano so abundantly that it was at one time collected commercially. It has also led to the foundation of an industry in Tuscany, where it is obtained from the soffioni of the Maremma. From Sasso in Tuscany it has received the name of sassolin or sassolite. Realgar, or arsenic sulphide, As 2 S 2, occurs in certain volcanic exhalations and is deposited as an orange-red incrustation, often associated with sulphur, as at the Solfatara, where orpiment, As2S3, has also been found.
Of all volcanic products, sulphur (q.v.) is in some respects the most important. .It may, in large quantity lining the walls of the crater, as at Popocatepetl in Mexico, where it was formerly worked by the Indian " volcaneros," or on the other hand it may be a rare product, as at Vesuvius.^ The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

.Sulphur appears generally to owe its origin in volcanic areas to the interaction of sulphur dioxide and sulphuretted hydrogen, or to the action of water on the latter.^ Defense officials who flew over the area in a helicopter said the surface of the water appeared red where the column was reported, which could indicate underwater volcanic activity, Shirai said.

A volcanic vent where sulphur is deposited is truly a solfatara (solfo terra) or a soufriere, but all volcanoes which have passed into that stage in which they emit merely heated vapours now pass under this name (see Solfatara). The famous Solfatara, an old crater in the Phlegraean Fields, exhales sulphurous vapours, especially at the Bocca Grande, from which sulphur is deposited. In the orangecoloured sulphur of the Solfatara, realgar may be present to the extent of as much as 18%. A brown seleniferous sulphur occurring at Vulcano, one of the Lipari Islands, was termed by W. Haidinger volcanite, but it should be noted that Professor W. H. Hobbs has applied this name to an anorthoclase-augite rock ejected as bombs at Vulcano. Sulphur containing selenium is known as a volcanic product in Hawaii, whilst in Japan not only selenium but tellurium occurs in certain kinds of sulphur.
.At the Solfatara, near Pozzuoli, the hot sulphurous vapours attack the trachytic rocks from which they issue, giving rise to such products as alum, kaolin and gypsum.^ "The distribution of underwater volcanoes tells us something about what is happening in the centre of the Earth," says John Hillier of the University of Cambridge in the UK. That is because they give information about the flows of hot rock in the mantle beneath.

To some of these products, including alunogen and mendozite (soda-alum), the name solfatarite was given by C. W. Sheppard in 1835. By prolonged action of the acid vapours on lava, the bases of the silicates may be removed, leaving the silica as a soft white chalk-like substance. The occurrence of kaolin and other white earthy alteration-products led to the hills around the Solfatara being known to the Romans as the Colli leucogei. The Hot Dust Cloud and Avalanche of Pele. - .The terrific eruptions in the islands of Martinique and St Vincent in the West Indies in 1902, furnished examples of a type of activity not previously recognized by vulcanologists, though, as Professor A. Lacroix has pointed out, similar phenomena have no doubt occurred elsewhere, especially in the Azores.^ No eruption has occurred yet, but seismic activity has commenced.

^ Seismic activity produced 155 events over the past 24 hours, which is similar to the previous day.

^ As compared to the eruption of 1956, the only one in the history of modern observations, the current eruption started in a more impetuous and powerful way the scientist pointed out.

By Drs Tempest Anderson and J. S. Flett, who were commissioned by the Royal Society to report on the phenomena, this type of explosive eruption is distinguished as the " Pelean type." Its distinctive character is found in the sudden emission of a dense black cloud of superheated and suffocating gases, heavily charged with incandescent dust, moving with great velocity and accompanied by the discharge of immense volumes of volcanic sand, which are not rained down in the normal manner, but descend like a hot avalanche. .The cloud, with the avalanche, is called by Lacroix a nuee Peleenne, or nuee ardente, the latter term having been applied to the fatal cloud in the eruptions at San Jorge in the Azores in 1818. In its typical form, the cloud seen at Pele appeared as a solid bank, opaque and impenetrable, but having the edge in places hanging like folds of a curtain, and apparently of brown or purplish colour.^ Clouds of white smoke are hanging over the area and continued earth tremors are keeping alive fears of another eruption.

Rolling along like an inky torrent, it produced in its passage intense darkness, relieved by vivid lightning. So much solid matter was suspended in the cloud, that it became too dense to surmount obstacles and behaved rather like a liquid. It has, however, been suggested that its peculiar movement as it swept down the mountain was due not simply to its heavy charge of solids, but partly to the oblique direction of the initial explosion. After leaving the crater, it underwent enormous expansion, and Anderson and Flett were led to suggest that possibly at the moment of emission it might have been partly in the form of liquid drops, which on solidifying evolved large volumes of gas held previously in occlusion. The deadly effect of the blast seems to have been mostly due to the irritation of the mucous membrane of the respiratory passages by the fine hot dust, but suffocating gases, like sulphur dioxide and sulphuretted hydrogen, were associated with the water-vapour. Possibly the incandescent dust was even hotter than the surrounding vapour, since the latter might be cooled by expansion.
It is said that the black cloud as it swept along was accompanied by an indraught of air, not however sufficiently powerful to check its rapid advance. The current of air was likened by Anderson and Flett to the inrush of air at a railway station as an express train passes. An attempt was made to determine the temperature of the fatal blast which destroyed St Pierre, but without very definite results. Thus it was assumed that as the telephone wires were not melted the temperature was below the fusing-point of copper: possibly, however, the blast may have passed too rapidly to produce the effects which might normally be due to its temperature.
.Shape of Volcanic Cones.^ It is popular with mountaineers and is seen as having one of the world's most perfect volcanic cone shapes.

- Those volcanic products which are solid when ejected, or which solidify after extrusion, tend to form by their accumulation around the eruptive vent a hill, which, though generally more or less conical, is subject to much variation in shape. It occasionally happens that the hill is composed wholly of ejected blocks, not themselves of volcanic origin. .In this case an explosion has rent the ground, and the effluent vapours have hurled forth fragments of the shattered rock through which the vent was opened, but no ash or other fragmentary volcanic material has been ejected, nor has any lava been poured forth.^ The presidential delegate for the region says an explosion has rocked the dome of the Chaiten volcano and sent volcanic material down the mountain's slope, threatening to block a river and cause flooding.

^ There have been no lava flows since the volcano began spitting out ash in December, he said.

^ A volcano erupted Saturday with little warning on a remote Aleutian island, sending residents of a nearby ranch fleeing from falling ash and volcanic rock.

This exceptional type is represented in the Eifel by certain monticules which consist mainly of fragments of Devonian slate, more or less altered. .In some cases the area within a ring of such rocky materials is occupied by a sheet of water, forming a crater-lake, known in the Eifel as a rnaar. Piles of fragmentary matter of this character, though containing neither cinders nor lava, may be fairly regarded as volcanic, inasmuch as they are due to the explosive action of hot subterranean vapours.^ In 1988 there was concern that the water levels in the lake were dropping, but this was due to overuse of water for hydroelectric generation power plant.

^ Mexico's Volcano of Fire, also known as the Colima volcano, is seen in a time exposure photograph during an explosion as lava and hot rocks flow down its sides and lightning flashes over its crater late June 1, 2005.

^ Lake Toba is a large caldera formed by volcanic and tectonic processes, and was the site of the world's most recent supervolcano 74,000 years ago.

In the ordinary paroxysmal type of eruption, however, cinders and ashes are shot upwards by the explosion and then descend in showers, forming around the orifice a mound, in shape rather like the diminutive cone of sand in the lower lobe of an hour-glass. .Little cindercones of this character may be formed within the crater of a large volcano during a single eruption; whilst large cones are built up by many successive discharges, each sheet of fragmentary material mantling more or less regularly round the preceding layer.^ The volcano, whose name means "Child of Krakatau," formed in the Sunda Strait close to Java island after Mount Krakatau's legendary eruption in 1883.

^ He says his findings may mean that researchers need to re-assess their understanding of how submarine volcanoes are formed .

^ The last eruption of Karthala volcano was in 1991 when an explosion occurred at Choungou-Chahal crater.

The symmetry of the hill is not infrequently affected by disturbing influences - a strong wind, for example, blowing the loose matter towards one side. The sides of a cinder cone have generally a steep slope, varying from 30 0 to 45°, depending on the angle of repose of the ejectamenta. .Excellent examples of small scoria-cones are found among the puys of Auvergne in central France, whilst a mag nificent illustration of this type of hill is furnished by Fusiyama, in Japan, which reaches an altitude of 12,000 ft.^ A lower level ash plume covering a large area drifted south at an altitude of 18,000 ft.

^ The Soufriere Hills volcano became active in 1995, and more than half the territory's 12,000 inhabitants moved away.

How such a cone may be rapidly built up was well shown by the formation of Monte Nuovo, near Pozzuoli - a hill 400 ft. high and a mile and a half in circumference, which is known from contemporary evidence to have been formed in the course of a few days in September 1538. The shape of a cinder cone may be retained for ages, since it is not liable to suffer greatly by denudation, as the rain soaks into the loose porous mass instead of running down the outside. .If lava rises in the duct of a cinder cone, it may, on accumulation in the crater, break down the wall, and thus effect its escape as a stream.^ The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

Cones breached in this way are not uncommon in Auvergne.
.It often happens that the cinders and ashes ejected from a volcano become mixed with water, and so form a paste, which sets readily as a hard tufaceous mass.^ Satellites can detect volcanoes that are more than 1500 m high because the mass of the submerged mountains causes gravity to pull the water in around them.

^ The beginning surge of water and rock debris often erodes rocks and vegetation from the side of a volcano and along the river valley it enters.

^ Back then a crack broke in the north-west slope of the volcano, with gases and ashes ejected.

Such natural tuff is indeed similar to the hydraulic cement known as pozzolana, which is formed artificially from volcanic ashes, and is renowned for durability. Although streams of volcanic mud are commonly associated with the ashes of a cinder-cone they may also form independent structures or tuffcones. These are generally broad-topped hills, having sides with an angle of slope as low in some cases as 15°.
.Lava-cones are built up of streams of lava which have consolidated around the funnel of escape.^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

^ Seismologists say the volcano is showing signs of a bulge in its cone, ndicating a build up of lava.

.Associated with the lava, however, there is usually more or less fragmentary matter, so that the cones are composite in structure and consequently more acute in shape than if they were composed wholly of lava.^ The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months.

^ Scientists have made their first expedition to the site of the eruption, which took place more than a week ago, and say the scene there is apocalyptic.

^ More hilly than the rest of Goma, its slopes served as a barrier to a lava flow at least two km (1.2 miles) wide.

.As the streams of lava in a volcano run at different times in different directions, they radiate from the centre, or flow from lateral or eccentric orifices, as irregular tongues, and do not generally form continuous sheets covering the mountain.^ Red hot molten rocks continued cascading down the Bonga gully while smaller flows and incandescent blocks of lava were observed entering adjacent gullies towards the general directions of Miisi village in Daraga town and Mabinit, Bonga, Matanag and Buyoan villages in this city.

^ Mexico's Volcano of Fire, also known as the Colima volcano, is seen in a time exposure photograph during an explosion as lava and hot rocks flow down its sides and lightning flashes over its crater late June 1, 2005.

^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

.When lava is the sole or chief element in the cone, the shape of the hill is determined to a great extent by the chemical composition and viscosity of the lava, its copiousness and the rapidity of flow.^ Previous eruptions have typically produced lava flows, but officials at the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.

^ ORIGINAL CAPTION : Superheated ash and lava is visible inside the cone of the Soufriere Hills volcano, which has been active lately, as seen from Olveston, Montserrat, on Jan.

.If the lava be highly basic and very mobile, it may spread to a great distance before solidifying, and thus form a hill covering a large area and rising perhaps to a great height, but remarkably flat in profile.^ A lower level ash plume covering a large area drifted south at an altitude of 18,000 ft.

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ The most useful instrument in observing the earth is employing a form of a very large radio telescope that stretches from border to border the electrical power grid.

Were the lava perfectly liquid, it would indeed form a sheet without any perceptible slope of surface. As a matter of fact, some lavas are so fluent as to run down an incline of 1 °, and flat cones of basalt have in some cases a slope of only 10° or even less. .The colossal mass of Mauna Loa, in Hawaii, forms a remarkably flat broad cone, spreading over a base of enormous area and rising to a height of 13,900 ft.^ The voluntary evacuation advisory covered the Mauna Loa Estates, Ohia Estates and Volcano Golf Course subdivisions as well as the Volcano Village and Keauhou Ranch areas.

^ Mauna Loa, Hawaii (Active!

.Major Dutton, writing in 1883, said that " a; moderate eruption of Mauna Loa represents more material than Vesuvius has emitted since the days of Pompeii."^ A major eruption in 1783 killed more than 1,000 people.

^ "This is going to be a human catastrophe," said an official from a contingent of UN ceasefire observers deployed in the eastern Congolese city of more than half a million.

^ Even though the eruption has continued for three days, scientists said it had lost little of its force.

Yet the lava is so mobile that it generally wells forth quietly, without explosive demonstration, and therefore unaccompanied by fragmentary ejectamenta. Fluent lavas like those of Hawaii are also poured forth from the volcanoes and volcanic fissures of Iceland.
If the lava be less basic and less fusible, the hill formed by its accumulation instead of being a low dome will take the shape of a cone with sides of higher gradient: in the case of andesite cones, for instance, the slope may vary from 25° to 35°. .Acid rocks, or those rich in silica, such as rhyolites and trachytes, may be emitted as very viscous lavas tending to form dome-shaped or bulbous masses.^ Volcanologists said the volcano appeared to be destroying a small lava dome which had formed in the crater since mid-November.

Experiment shows that such lavas may persist for a considerable time in a semi-solid condition. .It is possible for a dome to increase in size not by the lava running over the crater and down the sides but by injection of the pasty magma within the expanding bulb while still soft; or if solidified, the crust yields by cracking.^ That flurry of activity in turn came a week after lava spewed down one of its sides.

^ Mexico's Volcano of Fire, also known as the Colima volcano, is seen in a time exposure photograph during an explosion as lava and hot rocks flow down its sides and lightning flashes over its crater late June 1, 2005.

^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

Such a mode of growth, in which the dome consists of successive sheets that have been compared to the skins of an onion, has been illustrated by the experiments of Dr A. Reyer, and the structure is typically represented by the mamelons or steep-sided domes of the Isle of Bourbon. .The Puy-de-Dome in Auvergne is an example of a cone formed of the trachytic rock called from its locality domite, whilst the Grand Sarcoui in the same region illustrates the broad domeshaped type of hill.^ The so-called Volcano of Fire has been rumbling for the past week and scientists said it could erupt as pressure builds behind a dome that has formed inside its crater.

.Such domes may have no summit-crater, and it is then usually assumed that the top with the crater has been removed by denudation, but possibly in some cases such a feature never existed.^ The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

.The " dome volcano " of von Seebach is a dome of acid lava extruded as a homogeneous mass, without conspicuous chimney or crater.^ The dome, 213 feet tall, covers practically the entire 600-foot diameter of the volcano's crater.

^ Volcanologists said the volcano appeared to be destroying a small lava dome which had formed in the crater since mid-November.

^ The so-called Volcano of Fire has been rumbling for the past week and scientists said it could erupt as pressure builds behind a dome that has formed inside its crater.

.Although domes are usually composed of acid rocks, it seems possible that they may be formed also of basic lavas, if the magma be protruded slowly at a low temperature so as to be rapidly congealed.^ Volcanologists said the volcano appeared to be destroying a small lava dome which had formed in the crater since mid-November.

The Spine of Pele

A peculiar volcanic structure appeared at Mont Pele in the course of the eruption of 1902, and was the subject of careful study by Professor A. Lacroix, Dr E. A. Hoovey, A. Heilprin and other observers. It appears that from fissures in the floor of the Etang Sec a viscous andesitic lava, partly quartziferous, was poured forth and rapidly solidified superficially, forming a domeshaped mass invested by a crust or carapace. According to Lacroix, the crust soon became fractured, partly by shrinkage on consolidation and partly by internal tension, and the dome grew rapidly by injection of molten matter. Then there gradually rose from the dome a huge monolith or needle, forming a terminal spine, which in the course of its existence varied in shape and height, having been at its maximum in July 1903, when its absolute height was about 5276 ft. above sea-level. The walls of the spine, inclined at from 75° to 90° to the horizon, were apparently slickensided, or polished and scratched by friction: masses were occasionally detached and vapours were continually escaping. Several smaller needles were also formed. Some observers regarded the great spine as a solidified plug of lava from a previous outburst, expelled on a renewal of activity. .Lacroix, however, believed that it was formed by the extrusion of an enormous mass of highly viscid magma, perhaps partly solidified before emission, and he compared the formation of the dome in the crater to the structure on Santorin in 1866, described by Fouque as a " cumulo-volcano."^ Volcanologists said the volcano appeared to be destroying a small lava dome which had formed in the crater since mid-November.

^ The dome, 213 feet tall, covers practically the entire 600-foot diameter of the volcano's crater.

^ The so-called Volcano of Fire has been rumbling for the past week and scientists said it could erupt as pressure builds behind a dome that has formed inside its crater.

.Professor H. F. Cleland has suggested a comparison with the cone of andesite in the crater of the volcano of Toluca in Mexico, and it is said that similar formations have been observed in the volcanoes of the Andes.^ The Chaiten volcano has "probably been dormant for about 9,000 or 10,000 years but that's not unusual," said Charles Stern, a professor of volcanology at the University of Colorado who specializes in Andes volcanoes.

^ He said Thursday's eruption had produced some lava flows that did not extend far from the volcano's crater.

^ Volcanologists said the volcano appeared to be destroying a small lava dome which had formed in the crater since mid-November.

.Dr Tempest Anderson, on visiting Pele in 1907, found a stump of the spine, consisting of a kind of volcanic agglomerate, rising from a cone of talus formed of its ruins.^ The survey crew also found grayish mud rising up from the bottom of the ocean, but it was not immediately known whether any volcanic gases are being released.

The Crater

The eruptive orifice in normal volcano - the bocca of Italian vulcanologists - is usually situated at the bottom of a depression or cup, known as the crater. .This hollow is formed and kept open by the explosive force of the elastic vapours, and when the volcano becomes dormant or extinct it may be closed, partly by rock falling from its crumbling walls and partly by the solidification of the lava which it may contain.^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ On May 23 and May 30 the volcano, located in a sparsely populated rural area about 300 miles from Mexico City, belched lava and glowing rocks, but prompted no evacuations.

^ A volcano erupted Saturday with little warning on a remote Aleutian island, sending residents of a nearby ranch fleeing from falling ash and volcanic rock.

.If a renewed outburst occurs, the floor of the old crater may reopen or a new outlet may be formed at some weak point on the side of the mountain: hence a crater may, with regard to position, be either terminal or lateral.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

^ Some 12,000 residents of seven villages on the mountain's west side have been ordered to leave, said district official Edy Susanto.

^ Sunday, August 10, 2003 New crater lake forms at White Island Volcano...

The position of the crater will evidently be also changed on any shifting of the general axis of eruption. In shape and size the crater varies from time to time, the walls being perhaps breached or even blown away during an outburst. .Hence the height of a volcanic mountain in activity, measured to the rim of the crater or the terminal peak, is not constant.^ Etna is in an almost constant state of activity, but is not considered particularly dangerous and its slopes are home to farms and vineyards that make use of the rich volcanic soil.

^ Episodes of greater activity have ejected material beyond the crater rim.

.Vesuvius, for example, suffered a reduction of several hundred feet during the great eruption of 1906, the east side of the cone having lost, according to V. R. Matteucci, 120 metres.^ This happened once in 1989, when a 747 flew through an ash cloud from an eruption of the Redoubt volcano in Alaska, US. The engines stopped, causing the plane to lose several hundred feet in altitude.

^ The 800-metre-wide plateau inside the crater dropped 300 metres during the eruption, and islanders remain on high alert.

.Whilst in many cases the crater is a comparatively small circular hollow around the orifice of discharge, it forms in others a large bowllike cavity, such as is termed in some localities a " caldera."^ Lake Toba is a large caldera formed by volcanic and tectonic processes, and was the site of the world's most recent supervolcano 74,000 years ago.

^ Volcanologists said the volcano appeared to be destroying a small lava dome which had formed in the crater since mid-November.

.In the Sandwich Islands the craters are wide pits bounded by nearly vertical walls, showing stratified and terraced lavas and floored by a great plain of black basalt, sometimes with lakes of molten lava.^ Researchers on the island are concerned the recent activity may be creating more cracks lower down the volcano, which will allow the molten lava to spread further.

^ Sunday, August 10, 2003 New crater lake forms at White Island Volcano...

^ "The frequency of the tremors shows that a (lava) flow could happen in any part of the island."

Professor W. H. Pickering compares the lava-pits of Hawaii to the crater-rings in the moon. Some of the pit-craters in the Sandwich Islands are of great size, but none comparable with the greatest of the lunar craters. Dr G. K. Gilbert, however, has suggested that the ring-shaped pits on the moon are not of volcanic origin, but are depressions formed by the impact of meteorites. Similarly the " crater " of Coon Butte, near Canyon Diablo, in Arizona, which is 4000 ft. in diameter and 500 ft. deep, has been regarded as a vast pit due to collision of a meteorite of prodigious size. Probably the largest terrestrial volcanic crater is that of Aso-san, in the isle of Kiushiu (Japan), which is a huge oval depression estimated by some observers to have an area of at least zoo sq. m. .Some of the large pit-craters have probably been formed by subsidence, the cone of a volcano having been eviscerated by extravasation of lava, and the roof of the cavity having then subsided by loss of support.^ But while lava levels inside the crater have subsided, earth tremors have become more frequent.

^ Seismologists say the volcano is showing signs of a bulge in its cone, ndicating a build up of lava.

^ Sunday, August 10, 2003 New crater lake forms at White Island Volcano...

The term caldera has sometimes been limited to craters formed by such collapse.
.On the floor of the crater, ejected matter may accumulate as a conoidal pile; and if such action be repeated in the crater of the new cone, a succession of concentric cones will ultimately be formed.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

^ The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

^ Sunday, August 10, 2003 New crater lake forms at White Island Volcano...

.The walls of a perfect crater form a ring, giving the cone a truncated appearance, but the ring may suffer more or less destruction in the course of the history of the mountain.^ The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

A familiar instance of such change is afforded by Vesuvius. .The mountain now so called, using the term in a restricted sense, is a huge composite cone built up within an old crateral hollow, the walls of which still rise as an encircling rampart on the N. and N.E. sides, and are known as Monte Somma; but the S. and S.W. sides of the ancient crater have disappeared, having been blown away during some former outburst, probably the Plinian eruption of 79. In like manner the relics of an old crater form an amphitheatre partially engirdling the Soufriere in St Vincent, and other examples of " Somma rings " are known to vulcanologists.^ Mexico's Volcano of Fire, also known as the Colima volcano, is seen in a time exposure photograph during an explosion as lava and hot rocks flow down its sides and lightning flashes over its crater late June 1, 2005.

^ It said the eruption was not likely to threaten nearby towns, but traffic near the volcano was restricted.

^ This is the largest lake to have formed within this crater and has recently drowned the active vents.

.Much of the fragmental matter ejected from a volcano rolls down the inside of the crater, forming beds of tuff which incline towards the central axis, or have a centroclinal dip.^ As a consequence future eruptions will occur through the crater lake and, if ejected by eruptions, moderate volumes of water could flood down the Main Crater floor towards the sea.

^ Sunday, August 10, 2003 New crater lake forms at White Island Volcano...

^ Volcanologists said the volcano appeared to be destroying a small lava dome which had formed in the crater since mid-November.

.On the contrary, the sheets of cinder and lava which form the bulk of the cone slope away from the axis, or have a dip that is sometimes described as pericentric or qua-qua-versal.^ Several villages lie on its lower slopes, but the Italian government said yesterday that the lava was flowing away from them, and that there was no immediate danger.

According to the old " crater-of-elevation theory," held especially by A. von Humboldt, L. von Buch and Elie de Beaumont, this inclination of the beds was regarded as mainly due to upheaval. It was contended that the volcanic cone owed its shape, for the most part, to local distension of the ground, and was indeed comparable to a huge blister of the earth's crust, burst at the summit to form the " elevation crater." Palma, in the Canary Islands, was cited as a typical example of such a formation. This view was opposed mainly by Poulett-Scrope, Sir Charles Lyell and Constant Prevost, who argued that the volcano, so far from being bladder-like, was practically a solid cone of erupted matter: hence this view came to be known as the " crater-of-eruption theory." Its general soundness has been demonstfated whenever an insight has been obtained into the internal structure of a volcano. .Thus, after the eruption of Krakatoa in 1883 a magnificent natural section of the great cone of Rakata, at the S. end of the island, was exposed - the northern half having been blown away - and it was then evident that this mountain was practically a solid cone, built up of a great succession of irregular beds of tuff and lava, braced together by intersecting dykes.^ The volcano, whose name means "Child of Krakatau," formed in the Sunda Strait close to Java island after Mount Krakatau's legendary eruption in 1883.

^ It is popular with mountaineers and is seen as having one of the world's most perfect volcanic cone shapes.

^ Seismologists say the volcano is showing signs of a bulge in its cone, ndicating a build up of lava.

The internal architecture of a volcano is rarely so well displayed as in this case, but dissections of cones, more or less distinct, are often obtained by denudation. It should be mentioned that, in connexion with the structures called laccoliths, there may have been an elevation, or folding, and even faulting, of the superficial rocks by subterranean intrusion of lava; but this is different from the local expansion and rupture of the ground required by the old theory. .It may be noted, however, that in recent years the view of elevation, in a modified form, has not been without supporters.^ Lake Toba is a large caldera formed by volcanic and tectonic processes, and was the site of the world's most recent supervolcano 74,000 years ago.

.Where the growth of a volcanic mound takes place from within, as in certain steep-sided trachytic cones, there may be no perceptible crater or external outlet.^ The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

.Again, there are many volcanoes which have no crater at the summit, because the eruptions always take place from lateral outlets.^ There have been no deaths associated with the eruptions that began earlier this month, but thousands of villagers have been evacuated from the area.

^ The last eruption of Karthala volcano was in 1991 when an explosion occurred at Choungou-Chahal crater.

^ There are no indications of eruptive activity, but the volcano remains restless.

Even when a terminal pit is present, the lava may issue from the body of the mountain, and in some cases it exudes from so many vents or cracks that the volcano has been described as " sweating fire." Parasitic Cones. - .In the case of a lofty volcano the column of lava may not have sufficient ascensional force to reach the crater at the summit, or at any rate it finds easier means of egress at some weak spot, often along radial cracks, on the flanks of the mountain.^ The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

^ April 2005 deep volcanic = 7 events ; shallow volcanic = 5 events 16 April 2005 deep volcanic = 2 events ; shallow volcanic = 8 events 17 April 2005 deep volcanic = 0 events ; shallow volcanic = 2 events 18 April 2005 deep volcanic = 0 events ; shallow volcanic = 1 events It is still forbidden to visit the summit crater of Anak Krakatau volcano.

^ Stromboli Volcano (Italy) 38.79 N, 15.21 E, summit elevation 926 m, stratovolcano Strombolian activity continues from the northern summit crater.

.Thus at Etna, which rises to a height of more than io,800 ft., the eruptions usually proceed from lateral fissures, sometimes at least half-way down the mountain-side.^ The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months.

^ "This is going to be a human catastrophe," said an official from a contingent of UN ceasefire observers deployed in the eastern Congolese city of more than half a million.

^ Satellites can detect volcanoes that are more than 1500 m high because the mass of the submerged mountains causes gravity to pull the water in around them.

.When fragmental materials are ejected from a lateral vent a cinder-cone is formed, and by frequent repetition of such ejections the flanks of Etna have become dotted over with hundreds of scoria-cones much like the puys of Auvergne, the largest (Monte Minardo) rising to a height of as much as 750 ft.^ This is the largest lake to have formed within this crater and has recently drowned the active vents.

Hills of this character, seated on the parent mountain, are known as parasitic cones, minor cones, lateral cones, &c.
Such subordinate cones often show a tendency to a linear arrangement, rising from vents or bocche along the floor of a line of fissure. Thus in 1892 a chain of five cones arose from a rift on the S. side of Etna, running in a N. and S. direction, and the hills became known as the Monti Silvestri, after Professor Orazio Silvestri of Catania. .This rift, however,was but a continuation of a fissure from which there arose in 1886 the series of cones called the Monti Gemmellaro, while this in turn was a prolongation of a rent opened in 1883. The eruption on Etna in the spring of 1910 took place along the same general direction, but at a much higher elevation.^ Scientists have made their first expedition to the site of the eruption, which took place more than a week ago, and say the scene there is apocalyptic.

^ There are fissures opening up in the town which billow smoke.

The tendency for eruptions to be renewed along old lines of weakness, which can be readily opened afresh and extended, is a feature well known to vulcanologists. .The small cones which are frequently thrown up on lava streams were admirably exemplified on Vesuvius in the eruption of 1855 and figured by J. Schmidt.^ Since then, Grmsvtn volcano has produced a steady stream of ash and lava, with explosions sending ash up to 12,000m (40,000 feet) in the air.

^ Seismologists say the volcano is showing signs of a bulge in its cone, ndicating a build up of lava.

The name of " driblet cones " was given by J. D. Dana to the little cones and pillars formed by jets of lava projected from blowing holes at Kilauea, the drops of lava remaining plastic and cohering as they fell. Such clots may form columns and. pyramids, with almost vertical sides. Steep-sided cones more or less of this character occur elsewhere, but are usually built up around spiracles. Small cones formed by mere dabs of lava are known trivially as " spatter cones." Fissure Eruptions. - In certain parts of the world there are vast tracts of basaltic lava with little or no evidence of cones or of pyroclastic accompaniment. To explain their formation, Baron F. von Richthofen suggested that they represent great floods of lava which were poured forth not from ordinary volcanic craters with more or less explosive violence, but from great fissures in the earth's crust, whence they may have quietly welled forth and spread as a deluge over the surface of the country. The eruptions were thus effusive rather than explosive. Such phenomena, constituting a distinct type of vulcanism, are distinguished as fissure eruptions or massive eruptions - terms which suggest the mode of extrusion and the character of the extruded matter. As the lava in such outflows must be very fusible, it is generally of basaltic type, like that of Hawaii: indeed, the Hawaiian volcanoes, with their quiet emission of highly fluent lavas, connect the fissure eruptions with the " central eruptions," which are usually regarded as representing the normal type of activity. At the present day true fissure eruptions seem to be of rather limited occurrence, but excellent examples are furnished by Iceland. Here there are vast fields of black basalt, formed of sheets of lava which have issued from long chasms, studded in most cases with rows of small cones, but these generally so insignificant that they make no scenic features and might be readily obliterated by denudation. Dr T. Thoroddsen enumerates 87 great rifts and lines of cones in Iceland, and even the larger cones of Vesuvian type are situated on fissures.
It is believed that fissure eruptions must have played a far more important part in the history of the earth than eruptions of the familiar cone-and-crater type, the latter representing indeed only a declining phase of vulcanism. Sir Archibald Geikie, who has specially studied the subject of fissure eruptions, regards the Tertiary basaltic plateaus of N.E. Ireland and the Inner Hebrides as outflows from fissures, which may be represented by the gigantic system of dykes that form so marked a feature in the geological structure of the northern part of Britain and Ireland. These dykes extend over an area of something like 40,000 sq. m., while the outflows form an aggregate of about 3000 ft. in thickness. In parts of Nevada, Idaho, Oregon and Washington, sheets of late Tertiary basalt from fissure eruptions occupy an area of about 200,000 sq. m., and constitute a pile at least 2000 ft. thick. In India the " Deccan traps " represent enormous masses of volcanic matter, probably of like origin but of Cretaceous date, whilst South Africa furnishes other examples of similar outflows. Professor J. W. Gregory recognized in the Kapte plains of East Africa evidence of a type of vulcanism, which he distinguished as that of " plateau eruptions. " According to him a number of vents opened at the points of intersection of lines of weakness in a high plateau, giving rise to many small cones, and the simultaneous flows of lava from these cones united to form a far-spreading sheet.

Extrusive and Intrusive Magmas

When the molten magma in the interior of the earth makes its way upwards and flows forth superficially as a stream of lava, the product is described as extrusive, effusive, effluent or eruptive; but if, failing to reach the surface, the magma solidifies in a fissure or other subterranean cavity, it is said to be intrusive or irruptive. Rocks of the former group only are sometimes recognized as strictly " volcanic, " but the term is conveniently extended, at least in certain cases, to igneous rocks of the latter type, including therefore certain hypabyssal and even plutonic rocks.
When the intrusive magma has been forced into narrow irregular crevices it forms " veins, " which may exhibit complex ramifications, especially marked in some acid rocks; but when injected into a regularly shaped fissure, more or less parallel-sided, and cutting across the planes of bedding, it forms a wall-like mass of rock termed a " dyke. " Most dykes are approximately vertical, or at least highly inclined in position. The inclination of a dyke to a vertical plane is termed its " hade. " In a cinder-cone, the lava as it rises may force its way into cracks, formed by pressure of the magma and tension of the vapours, and will thus form a system of veins and dykes, often radiating from the volcanic axis and strengthening the structure by binding the loose materials together. Thus, in the Valle del Bove, a huge cavity on the east side of Etna, the walls exhibit numerous vertical dykes, which by their hardness stand out as rocky ribs, forming a marked feature in the scenery of the valley. In a similar way dykes traverse the walls of the old crater of Monte Somma at Vesuvius. Exceptionally a dyke may be hollow, the lava having solidified as a crust at the margin of the fissure but having escaped from the interior while still liquid.
When molten matter is thrust between beds of tuff or between successive lava-flows or even ordinary sedimentary strata, it forms an intrusive sheet of volcanic rock known as a " sill. " A sill may sometimes be traced to its connexion with a dyke, which represents the channel up which the lava rose, but instead of reaching the surface the fluid found an easier path between the strata or perhaps along a horizontal rent. Although a dyke may represent a conduit for the ascent of lava which has flowed out superficially, yet if the lava has been removed at the surface by denudation the dyke terminates abruptly, so that its function as the former feeder of a lava-current is not evident. In other cases a dyke may end bluntly because the crack which it occupies never reached the surface.
Lava which has insinuated itself between planes of stratification may, instead of spreading out as a sheet or sill, accumulate locally as a lenticular mass, known as a laccolith or laccolite. Such a mass, in many cases rather mushroom-shaped, may force the superincumbent rocks upwards as a dome, and though at first concealed may be ultimately exposed by removal of the overlying burden by erosion. The term phacolite was introduced by A. Harker to denote a meniscus-shaped mass of lava intruded in folded strata, along a crest or a trough. The bysmalith of Professor Iddings is a laccolith of rather plug-like shape, with a faulted roof. An intrusive mass quite irregular in shape has been termed by R. A. Daly a chonolith (Gr. xc. vn, a mould), whilst an intrusion of very great size and illdefined form is sometimes described as a bathylith or batholite. Structural Peculiarities in Lava. - Many of the structures exhibited by lava are due to the conditions under which solidification has been effected. A dyke, for example, may be vitreous at the margin where it has been rapidly chilled by contact with the walls of the fissure into which it was injected, whilst the main body may be lithoidal or crystalline: hence a basalt dyke will sometimes have a selvage formed of the basaltic glass known as tachylyte. A similar glass may form a thin crust on certain lava-flows. In a homogeneous vitreous lava, contraction on solidification may develop curved fissures, well seen in the delicate " perlitic " cracks of certain obsidians, indicating a tendency to assume a globular structure. This structure becomes very distinct by the development of " spherulites, " or globular masses with a radiating fibrous structure, sometimes well seen in devitrified glass. Occasionally the spherulitic bodies in lava are hollow, when they are known as lithophyses, of which excellent examples occur at Obsidian Cliff in the Yellowstone National Park, as described by Professor Iddings. Globular structure on a large scale is sometimes displayed by lavas, expecially those of basic type, such as the basalt of Aci Castello in Sicily, which was probably formed, according to Professor Gaetano Platania, by flow of the lava into submarine silt, relics of which still occur between the spheroids. Ellipsoidal or pillow-shaped masses are not infrequently developed in ancient lava-flows, and Sir A. Geikie has suggested the term " pillow-structure " for such formations. Dr T. Anderson has observed them in the recent lavas of Savaii.
Joints, or cracks formed by shrinkage on solidification, may divide a sheet of lava into columns, as familiarly seen in basalt, where the rock often consists of a close mass of regular polygonal prisms, mostly hexagonal. Each prism is divided at intervals by transverse joints, more or less curved, so that the portions are united by a slight ball-and-socket articulation. As the long axes of the columns lie at right angles to the cooling surface they are vertical in a horizontal sheet of lava, horizontal in a vertical dyke, and inclined or curved in other cases. It sometimes happens that in a basaltic dyke the formation of the prisms, having started from the opposite walls as chilling surfaces, has not been completed; and hence the prisms fail to meet in the middle. A spheroidal structure is often developed in basalt columns by weathering, the rock exfoliating in spherical shells, rather like the skins of an onion: such a structure is characteristically shown at the Kasekellar, known also as the Elfen Grotto, at Bertrich, near Alf on the Mosel, where the pillars of the lava are broken into short segments which suggest by their flattened globular shape a pile of Dutch cheeses. Although prismatic jointing, or columnar structure, is most common in basalt, it occurs also in other volcanic rocks. Fine columns of obsidian, for instance, are seen at Obsidian Cliff in the Yellowstone Park, where the pillars may be 50 ft. or more in height. Such an occurrence, however, is exceptional.
Vitreous lavas often show fluxion structure in the form of streaks, bands or trains of incipient crystals, indicating the flow of the mass when viscous. The character of this structure is related to the viscosity of the lava. Those structural peculiarities which depend mainly on the presence of vapour, such as vesiculation, have been already noticed, and the porphyritic structure has likewise been described.
Submarine Volcanoes. Considering how large a proportion of the face of the earth is covered by the sea, it seems likely that 'volcanic eruptions must frequently occur on the ocean-floor. When, as occasionally though not often happens, the effects of a submarine eruption are observed during the disturbance, it is seen that the surface of the sea is violently agitated, with copious discharge of steam; the water passes into a state of ebullition, perhaps throwing up huge fountains; shoals of dead fishes, with volcanic cinders, bombs and fragments of pumice, float around the centre of eruption, and ultimately a little island may appear above sea-level. This new land is the peak of a volcanic cone which is based on the sea-floor, and if in deep water the submarine mountain must evidently be of great magnitude. Christmas Island in the Indian Ocean, described by Dr C. W. Andrews, appears to be a volcanic mountain, with Tertiary limestones,. standing in water more than 14,000 ft. deep. Many volcanic islands, such as those abundantly scattered over the Pacific, must have started as submarine volcanoes which reached the surface either by continued upward growth or by upheaval of the sea-bottom. Etna began its long geological history by submarine eruptions in a bay of the Mediterranean, and Vesuvius in like manner represents what was originally a volcano on the sea-floor. As the ejectamenta from a submarine vent accumulate on the sea-bottom they become intermingled with relics of marine organisms, and thus form fossiliferous volcanic tuffs. By the distribution of the ashes over the sea-floor, through the agency of waves and currents, these tuffs may pass insensibly into submarine deposits of normal sedimentary type.
One of the best examples of a submarine eruption resulting in the formation of a temporary island occurred in 1831 in the Mediterranean between Sicily and the coast of Africa, where the water was known to have previously had a depth of too fathoms. After the usual manifestations of volcanic activity an accumulation of black cinders and ashes formed an island which reached at one point a height of 200 ft., so that the pile of erupted matter had a thickness of about 800 ft. The new island, which was studied by Constant Prevost, became known in England as Graham's Island, in France as Ile Julie and in Italy by various names as Isola Ferdinandea. Being merely a loose pile of scoriae, it rapidly suffered erosion by the sea, and in about three months was reduced to a shoal called Graham's Reef. In 1891 a submarine eruption occurred near the isle of Pantellaria in the same waters, and the eruptive centre was termed by Professor H. S. Washington and Foerstner volcano, but it gave rise to no island. A well-known instance of a temporary volcanic island was furnished by Sabrina - an islet of cinders thrown up by submarine eruptions in 1811, off the coast of St Michael's, one of the Azores. The island of Bogosloff, or Castle island, in Bering Sea, about 40 m. W. of Unalaska Island, is a volcanic mass which was first observed in 1796 after an eruption. In 1883 another eruption in the neighbouring water threw up a new volcanic cone of black sand and ashes, known as New Bogosloff or Fire Island, situated about half a mile to the N.W. of Old Bogosloff, with which it was connected by a low beach. Another island, called Perry Island, larger than either of the others, made its appearance in the neighbourhood about the time of the great earthquake in California in 1906. It is reported that some of these islands have since disappeared.
Mud Volcanoes. Mud volcanoes are small conical hills of clay which discharge, more or less persistently, streams of fine mud, sometimes associated with naphtha or petroleum, and usually with bubbles of gas. As the mud is generally saline, the hills are known also as " salses." The gases are chiefly hydrocarbons, often with more or less sulphuretted hydrogen and carbon dioxide, and sometimes with nitrogen. Though generally less than a yard in height, the cones may in exceptional cases rise to an elevation of as much as Soo ft. The mud oozes from the top and spreads over the sides, or is spurted forth with the gases. Occasionally the discharge is vigorous, mud and stones being thrown up to a considerable height, sometimes accompanied by flames due to combustion of the hydrocarbons.
Mud volcanoes occur in groups, and have a wide distribution. They are known in Iceland; in Modena; at Taman and Kertch, in the Crimea; at Baku on the Caspian; in Java and in Trinidad: Humboldt described those near Turbaco, in Colombia. In Sicily they occur near Girgenti, and a group is known at Paterno on Etna. Bythe Sicilians they are termed, maccalube, a word of Arabic origin. The " paint-pots " of the Yellowstone National Park are small mud volcanoes.
Many, so-called mud volcanoes appear to be due to the derangement of subterranean water-flow or to landslips in connexion with earthquakes, whilst others may be referable to certain chemical reactions going on underground; but there are others again which seem to be truly of volcanic origin. Hot water and steam escaping through clays, or crumbling tuffs reduced to a clayey condition, may form conical mounds of pasty material, through which mud oozes and water escapes.
Geysers are closely related to volcanoes, but in consequence of their special interest they are treated separately (see Geyser). For natural steam-holes and other phenomena connected with declining vulcanicity, see Soffioni, Solfatara and Mofetta.
Geographical Distribution of Volcanoes. It is matter of frequent observation that volcanoes are most abundant in regions marked by great seismic activity. Although the volcano and the earthquake are not usually connected in the direct relation of cause and effect, yet in many cases they seem referable to a common origin. Both volcanic extrusion and crustal movement may be the means of relieving local strains in the earth's crust, and both are found to occur, as might reasonably be expected, in many parts of the earth where folding and fracture of the rocks have frequently happened and where mountain-making appears to be still in progress. Thus, volcanoes may often be traced along zones of crustal deformation, or folded mountain-chains, especially where they run near the borders of the oceanic basins. They are frequently associated with the Pacific type of coast-line.
The most conspicuous example of linear distribution is furnished by the great belt of volcanoes, coinciding for the most part with a band of seismic disturbance, which engirdles intermittently the huge basin of the Pacific; though here, as elsewhere in studying volcanic topography, regard must be paid to dormant and extinct centres as well as to those that are active at the present time. As volcanoes are in many cases ranged along what are commonly regarded as lines of fracture, it is not surprising that the centres of most intense vulcanicity are in many cases situated at the intersection of two or more fracture-lines. On the eastern side of the Pacific Ocean the great volcanic ring may be traced, though with many and extensive interruptions, from Cape Horn to Alaska. In South America the chain of the Andes between Corcovado in the south and Tolima in the north is studded at irregular intervals with volcanoes, some recent and many more extinct, including the loftiest volcanic mountains. in the world. The grandest group of South American volcanoes, though mostly quiescent, is in Ecuador. Cotopaxi, seen in activity by E. Whymper in 1880, has, according to him, a height of 19,613 ft., whilst Sangay is said to be one of the most active volcanoes in the world. The linear arrangement, often a marked feature in the distribution of volcanoes, is well exemplified in the general north-andsouth trend of the Andean ranges, the volcanoes being situated along the orographic axis. These folded mountains with their volcanoes also illustrate the close relationship to the sea so frequently observed in volcanic topography, a relationship, however, not without many exceptions. The volcanic rock called andesite was so named by L. von Buch from its characteristic occurrence in the Andes. It is notable that the volcanic rocks throughout the great Pacific belt present much similarity in composition. The volcanoes of Ecuador have been described in detail by A. Stiibel and others (see Andes).
Central America contains a large number of active volcanoes and solfataras, many of which are located in the mountains parallel to the western coast. Conseguina, on the south side of the Gulf of Fonseca, is remarkable for its eruption in 1835, when an enormous, volume of ash was ejected and the summit of the mountain blown away. Izalco, in San Salvador, came into existence in 1770, and is habitually active. In the centre of Lake Ilopango in Salvador,. which possibly occupies an ancient crater, a volcanic island arose in 1880 and attained a height of 160 ft. Guatemala is peculiarly rich in volcanoes, as described by Dr Tempest Anderson, who visited the country in 1907. The Cerro Quemado, or the Volcano of Quezaltenango, was the scene of a great eruption in 1785. At the Volcano of Santa Maria there was an outburst in 1902 more violent than the simultaneous eruptions in the Lesser Antilles. The cones of Guatemala include the Volcan de Fuego and the Volcan de Agua, the former often active in historic times, whilst the latter is notable for the flood which in 1541 swept down from the mountain and destroyed Old Guatemala, but this flood was probably not of volcanic origin.
The plateau of Mexico is the seat of several active volcanoes which occur in a band stretching across the country from Colima in the west to Tuxtla near Vera Cruz. The highest of these volcanic mountains is Orizaba, or Cithaltepetl, rising to an altitude of 18,200 feet, and known to have been active in the 16th century. Popocatepetl (" the smoking mountain ") reaches a height of about. 17,880 ft., and from its crater sulphur was at one time systematically collected. The famous volcano of Jorullo, near Toluca, at a distance of about 120 m. from the sea, has been the centre of much scientific discussion since it was regarded by Humboldt, who visited it in 1803, as a striking proof of the elevation theory. It came into existence rapidly during an eruption which began in September 1759, when it was said by unscientific observers that the ground became suddenly inflated from below. The cone, though not of exceptional magnitude, is situated in an elevated district, and its summit rises to about 4330 ft. above sea-level. In the neighbourhood of Jorullo there are three subordinate cones of similar character known as volcancitos, with great numbers of small mounds of cinder and ash formed around fumaroles on the lava, and locally called hornitos, or " little ovens. " The streams of basaltic lava from Jorullo form rough barren surfaces, which pass under the name of malpays, or bad lands.
In the United States very few volcanoes are active at the present day, though many have become extinct only in times that are geologically recent. An eruption occurred in 1857 at Tres Virgines, in the south of California, and the cinder cone on Lassen's Peak (California) was also active in the middle of the 19th century. The Mono Valley craters and Mount Shasta, in California, are extinct. The Cascade Range contains numerous volcanic peaks, but only few show signs of activity. 1Vlount Hood, in Oregon, exhales vapour, as also does Mount Rainier in Washington. Mount St Helens (Washington) was in eruption in 1841 and 1842; and Mount Baker (Washington), the most northern of the volcanoes connected with the Cascade Range, is said to have been active in 1843. Few volcanic peaks occur in the Rocky Mountains, but evidence of lingering activity is very marked in the geysers and hot springs of the Yellowstone National Park. The earth's internal heat is also manifested at many points elsewhere, as at Steamboat Springs on the Virginia Range, an offshoot of the Sierra Nevada, and in the Comstock Lode.
Volcanic activity is prominent in Alaska, along the Coast Range and in the neighbouring islands. The crater of Mount Edgecumbe, in Lazarus Island, is said to have been active in 1796, but this is doubtful. Mount Fairweather has probably been in recent activity, and the lofty cone of Mount Wrangell, on Copper river, is reported to have been in eruption in 1819. In the neighbourhood of Cook's Inlet there are several volcanoes, including the island of St Augustine. Unimak Island has two volcanoes, which have supplied the natives, with sulphur and obsidian; one of these volcanoes being Mount Shishaldin, a cone rivalling Fusiyama in graceful contour. The.
Aleutian volcanic belt is a narrow, curved chain of islands, extending from Cook's Inlet westwards for nearly 1600 m. It is notable that the convexity of the curve faces the great ocean, as has been observed in other cases, the arcs following the direction of the rock-folds. According to Professor I. C. Russell, an authority on the volcanoes of N. America, there are in the Aleutian Islands and in the peninsula no fewer than 57 craters, either active or recently extinct.
From the Aleutian Islands the volcanic band of the Pacific changes its direction, and passing to the peninsula of Kamschatka, where 14 volcanoes are said to be active, turns southwards and forms the festoon of the Kurile Islands. Here again the convexity of the insular arc is directed towards the ocean. This volcanic archipelago leads on to the great islands of Japan, where the volcanoes have been studied by Professor J. Milne, who also described those of the Kuriles. Of the 54 volcanoes recognized as now active or only recently extinct in Japan, the best known is the graceful cone of the sacred mountain Fusiyama, but others less pretentious are far more dangerous. The great eruption of Bandaisan, about 120 m. N. of Tokio, which occurred in 1888, blew off one side of the peak called Kobandai, removing, according to Professor Sekiya's estimate, about 2982 million tons of material. Aso-san in Kiushui, the southernmost large island of Japan, is notable for the enormous size of its crater. In the Bonin group of islands volcanic activity is indicated by such names as Volcano Island and Sulphur Island.
South of the Japanese archipelago the train of volcanoes passes through some small islands in or near the Loo Choo (Liu Kiu) group and thence onwards by Formosa to the Philippine Islands, where subterranean activity finds abundant expression in earthquakes and volcanoes. After leaving this region the linear arrangement of the eruptive centres becomes less distinctly marked, for almost every island in the Moluccas and the Sunda Archipelago teems with volcanoes, solfataras and hot springs. Possibly, however, a broken zone may be traced from the Moluccas through New Guinea and thence to New Zealand, perhaps through eastern Australia (for though no active volcanoes are known there, relics of comparatively recent activity are abundant); or again by way of the Bismarck Archipelago, the Solomon Islands, the New Hebrides, the Fiji Islands and Kermodoc Island.
The great volcanic district in New Zealand is situated in the northern part of North Island, memorable for the eruption of Tarawera in 1886. This three-peaked mountain on the south side of Lake Tarawera, not previously known to have been active, suddenly burst into action; a huge rift opened, and Lake Rotomahana subsided, with destruction of the famous sinter terraces. The crater of Tongariro is in the solfatara stage, whilst Mount Ruapehu is regarded as extinct. On White Island in the Bay of Plenty the cone of Wharkari is feebly active.
Far to the south, on Ross Island, off South Victoria Land, in Antarctica, are the volcanoes of Erebus and Terror, the former of which is active. These are often regarded as remotely related to the Pacific zone, but Dr G. T. Prior has shown that the Antarctic volcanic rocks which he examined belonged to the Atlantic and not the Pacific type.
Within the great basin of the Pacific, imperfectly surrounded by its broken girdle of volcanoes, there is a vast number of scattered islands and groups of islands of volcanic origin, rising from deep water, and hiving in many cases active craters. The most important group is the Hawaiian Archipelago, where there is a chain of at least fifteen large volcanic mountains - all extinct, however, with the exception of three in Hawaii, namely Mauna Loa, Kilauea and Hualalai; and of these Hualalai has been dormant since 1811. It is notable that the two present gigantic centres of activity, though within 20 m. of each other, appear to be independent in their eruptivity. Several of the Hawaiian Islands, as pointed out by J. D. Dana, who was a very high authority on this group, consist of two volcanoes united at the base, forming volcanic twins or doublets.
The volcanic regions of the Pacific are connected with those of the Indian Ocean by a grand train of islands rich in volcanoes, stretching from the west of New Guinea through the Moluccas and the Sunda Islands, where they form a band extending axially through Java and Sumatra. Here is situated the principal theatre of terrestrial vulcanicity, apparently representing an enormous fissure, or system of fissures, in the earth's crust, sweeping in a bold curve, with its convexity towards the Indian Ocean.
Numerous volcanic peaks occur in the string of small islands to the east of Java - notably in Flores, Sumbawa, Lombok and Bali; and one of the most terrific eruptions on record in any part of the world occurred in the province of Tomboro, in the island of Sumbawa, in the year 1815. Java contains within its small area as many as 49 great volcanic mountains - active, dormant and extinct. The largest is Smerin, about 12,000 ft. high, but the most regularly active is said to be Gownong Lamongang, which is in almost uninterrupted activity, emitting usually only ashes and vapour, though in 1883 lava streamed forth. Many of the Javanese volcanoes present marked regularity of contour, with the sides of the cones rather symmetrically furrowed by tropical rains and probably ridged by ash-slides. The radial furrows on volcanic cones are sometimes known as " barrancos." The little uninhabited island of Krakatoa in the Strait of Sunda appears to be situated at a volcanic node, or the intersection of two curved fissures, and it is believed that the island itself represents part of the basal wreck of what was once a volcano of gigantic size. After two centuries of repose, a violent catastrophe occurred in 1883, whereby the greater part of the island was blown away. This eruption and its effects were made the subject of careful study by Verbeek, B g on and Judd.
Through the great island of Sumatra, a chain of volcanoes runs longitudinally, and may possibly be continued northwards in the Bay of Bengal by Barren Island and Norcondam - the former an active and the latter an extinct volcano. On the western side of the Indian Ocean a small volcanic band may be traced in the islands of the Mascarene group, several craters in Reunion (Bourbon) being still active. Far south in the Indian Ocean are the volcanic islands of New Amsterdam and St Paul. The Comoro Islands in the channel of Mozambique exhibit volcanic activity, whilst in East and Central Africa there are several centres, mostly extinct but some partially active, associated with the Rift Valleys. The enormous cones of Kenia and Kilimanjaroo are extinct, but on Kibo, one of the summits of the latter, a crater is still preserved. The Mfumbiro volcanoes, S. of Lake Edward, rise to a height of more than 14,700 feet. Kirunga, N. of Lake Kivu, is still partially active. Elgon is an old volcanic peak, but Ruwenzori is not of volcanic origin. On the west side of Africa, the Cameroon Peak is a volcano which was active in 1909, and the island of Fernando Po is also volcanic. Along the Red Sea there are not wanting several examples of volcanoes, such as Jebel Teir. Aden is situated in an old crater.
Passing to the Atlantic, a broken band of volcanoes, recent and extinct, may be traced longitudinally through certain islands, some of which rise from the great submarine ridge that divides the ocean, in part of its length, into an eastern and a western trough. The northern extremity of the series is found in Jan Mayen, an island in the Arctic Ocean, where an eruption occurred in 1818. Iceland, however, with its wealth of volcanoes and geysers, is the most important of all the Atlantic centres. According to Dr T. Thoroddsen there are in Iceland about 130 post-glacial volcanoes, and it is known that from 25 to 30 have been in eruption during the historic period. Many of the Icelandic lava-flows, such as the immense flood from Laki (Skapta Jokull) in 1783, are referable to fissure eruptions, which are the characteristic though not the exclusive form of activity in this island. Probably this type was also responsible for the sheets of old lava in the terraced hills of the Faroe Islands, to which may have been related the Tertiary volcanoes of the west of Scotland and the north of Ireland.
An immense gap separates the old volcanic area of Britain from the volcanic archipelagoes of the Azores, the Canaries and the Cape Verd Islands. Palma - a little island in the Canary group, with a caldera or large crater at its summit, from which fissures or barrancos radiate - is famous in the history of vulcanology, in that it furnished L. von Buch with evidence on which he founded the " crater-ofelevation " theory. The remaining volcanic islands of the Atlantic chain, all now cold and silent, include Ascension, St Helena and Tristan da Cunha, whilst in the western part of the South Atlantic are the small volcanic isles of Trinidad and Ferdinando do Noronha. St Paul's rocks appear also to be of volcanic origin.
One of the most important volcanic regions of the world is found in the West Indies, where the Lesser Antilles - the scene of the great catastrophes of 1902 - form a string of islands, stretching in a regular arc that sweeps in a N. and S. direction across the eastern end of the Caribbean Sea. Subject to frequent seismic disturbance, and rich in volcanoes, solfataras and hot springs, these islands seem to form the summit of a great earth-fold which, rising as a curved ridge from deep water, separates the Caribbean Sea from the Atlantic. The volcanoes are situated on the inner border of the curve. It is notable that the Antilles and the Sunda Islands, two of the grandest theatres of vulcanicity on the face of the earth, are situated at the antipodes of each other - one being apparently an eastern and the other a western offshoot of the great Pacific girdle.
The European volcanoes, recent and extinct, may be regarded as representing rather ill-defined branches thrown off eastwards from the Atlantic band. Vesuvius is the only active volcano on the mainland, but in the Mediterranean there are Etna on the coast of Sicily; the Lipari Islands, with Stromboli and Vulcano in chronic activity; and farther to the east the archipelago of Santorin, where new islands have appeared in historic times. Submarine eruptions have occurred also between Sicily and the coast of Africa; one in 1831 having given rise temporarily to Graham's Island, and another in 1891 appearing near Pantellaria, itself a volcanic isle. Of the extinct European volcanoes, some of the best known are in Auvergne, in the Eifel, in Bohemia and in Catalonia, whilst the volcanic land of Italy includes the Euganean hills, the Alban hills, the Phlegraean Fields, &c. The great lakes of Bolsena and Bracciano occupy old craters, and many smaller sheets of water are on similar sites. The volcanic islands no longer active include Ischia, with the great cone of Epomeo which was in a state of eruption in 1301; the Ponza Islands, Nisida, Vivera and others near Naples; and several in the Greek archipelago, such as Milos, Kimolos and Polinos.
From the eastern end of the Mediterranean evidence of former volcanic activity may be traced into Asia Minor and thence to Armenia and the Caucasus. East of Smyrna there is a great desolate tract which the ancients recognized as volcanic and termed the Catacecaumene (burnt country). The volcanic districts of Lydia were studied by Professor H. S. Washington. In the plateau of Armenia there are several extinct volcanic mountains, more or less destroyed, of which the best known is Ararat. Nimrud Dagh on the shore of Lake Van is said to have been in eruption in the year 1441. Dr F. Oswald has described the volcanoes of Armenia. Of the volcanoes in Persian territory not now active, Demavend, south of the Caspian, is an important example. Elburz is also described as an old volcano. It has been said that in Central Asia there are certain vents still active, and recent volcanic rocks are known from the Przhevalsky chain and other localities.
The number of volcanoes known to be actually active on the earth is generally estimated at between 300 and 400, but there is reason to believe that this estimate is far too low. If account be taken of those volcanic cones which have not been active in historic time, the total will probably rise to several thousands. The distribution of volcanoes at various periods of the earth's history, as revealed by the local occurrence of volcanic rocks at different horizons in the crust of the earth, is discussed under Geology. Periods of great earthmovement have been marked by exceptional volcanic activity.
Causes of Vulcanicity. In discussing the cause of vulcanicity two problems demand attention: first the origin of the heat necessary for the manifestation of volcanic phenomena, and secondly the nature of the force by which the heated matter is raised to the surface and ejected. According to the old view, which assumed that the earth was a spheroid of molten matter invested by a comparatively thin crust of solid rock, the explanation of the phenomena appeared fairly simple. The molten interior supplied the heated matter, while the shrinkage of the cooling crust produced fractures that formed the volcanic channels through which it was assumed the magma might be squeezed out in the process of contraction. When physicists urged the necessity of assuming that the globe was practically solid, vulcanologists were constrained to modify their views. Following a suggestion of W. Hopkins of Cambridge, they supposed that the magma, instead of existing in a general central cavity, was located in comparatively small subterranean lakes. Some authorities again, like the Rev. O. Fisher, regarded the magma as constituting a liquid zone, intermediate between a solid core and a solid shell.
If solidification of the primitive molten globe proceeded from the centre outwards, so as to form a sphere practically solid, it is conceivable that portions of the original magma might nevertheless be retained in cavities, and thus form " residual lakes." Although the mass might be for the most part solid, the outer portion, or " crust," could conceivably have a honeycombed structure, and any magma retained in the cells might serve indirectly to feed the volcanoes. Neighbouring volcanoes seem in some cases to draw their supply of lava from independent sources, favouring the idea of local cisterns or "intercrustal reservoirs." It is probable, however, that subterranean reservoirs of magma, if they exist, do not represent relics of an original fluid condition of the earth, but the molten material may be merely rock which has become fused locally by a temporary development of heat or more likely, by a relief of pressure. It should be noted that the quantity of magma required to supply the most copious lava-flows is comparatively small, the greatest recorded outflow (that of Tomboro in Sumbawa, in 1815) not having exceeded, it is said, six cubic miles; and even this estimate is probably too high. Whilst in many cases the magma-cisterns may be comparatively small and temporary, it must be remembered that there are regions where the volcanic rocks are so similar throughout as to suggest a common origin, thus needing intercrustal reservoirs of great extent and capacity. It has been suggested that comparatively small basins, feeding individual volcanoes, may draw their supply from more extensive reservoirs at greater depths.
Much speculation has been rife as to the source of the heat required for the local melting of rock. Chemical action has naturally been suggested, especially that of superficial water, but its adequacy may be doubted. After Sir Humphry Davy's dis covery of the metals of the alkalis, he thought that their remarkable behaviour with water might explain the origin of subterranean heat; and in more recent years others have seen a local source of heat in the oxidation of large deposits of iron, such as that brought up in the basalt of Disco Island in Greenland. It has been assumed by Moissan and by Gautier that water might attack certain metallic carbides, if they occur as subterranean deposits, and give rise to some of the products characteristic of volcanoes. But it seems that all such action must be very limited, and utterly inadequate to the general explanation of volcanic phenomena. At the same time it must be remembered that access of water to a rock already heated may have an important. physical effect by reducing its melting point, and may thus greatly assist in the production of a supply of molten matter. The admission of surface-waters to heated rocks is naturally regarded as an important source of motive power in consequence of the sudden generation of vapour, but it is doubtful to what extent it may contribute, if at all, to the origin of volcanic heat.
According to Robert Mallet a competent source of subterranean heat for volcanic phenomena might be derived from the transformation of the mechanical work of compressing and crushing parts of the crust of the earth as a consequence of secular contraction. This view he worked out with much ingenuity, supporting it by mathematical reasoning and an appeal to experimental evidence. It was claimed for the theory that it explained the linear distribution of volcanoes, their relation to mountain chains, the shallow depth of the foci and the intermittence of eruptive activity. A grave objection,. however, is the difficulty of conceiving that the heat, whether due to crushing or compression, could be concentrated locally so as to produce a sufficient elevation of temperature for melting the rocks. According to the calculations of Rev. O. Fisher, the crushing could not, under the most favourable circumstances, evolve heat enough to account for volcanic phenomena.
Since pressure raises the melting-point of any solid that expands on liquefaction, it has been conjectured that many deep-seated rocks, though actually solid, may be potentially liquid; that is, they are maintained in a solid state by pressure: only. Any local relief of pressure, such as might occur in the folding and faulting of rocks, would tend, without further accession of heat, to induce fusion. But although moderate pressure raises the fusing-point of most solids, it is believed,, from modern researches, that very great pressures may have a contrary effect.
It is held by Professor S. Arrhenius that at great depths in. the earth the molten rock, being above its critical point, can. exist only in the gaseous condition; but a gas under enormous pressure may behave, so far as compressibility is concerned, like a rigid solid. He concludes, from the high density of the earth as a whole and from other considerations, that the central part of our planet consists of gaseous iron (about 80% of the earth's diameter) followed by a zone of rock magma in a gaseous condition (about 15%), which passes insensibly outwards into liquid rock (4%), covered by a thin solid crust (less than i % of diameter). If water from the crust penetrates by osmosis through the sea-floor to the molten interior, it acts, at the high temperature, as an acid, and decomposes the silicates of the magma. The liquid rock, expanded and rendered more mobile by this water, rises in fissures, but in its ascent suffers cooling, so that the water then loses its power as an acid and is displaced by silicic acid, when the escaping steam gives rise to the explosive phenomena of the volcano. The mechanism of the volcano is therefore much like that of a geyser, a comparison. long ago suggested by Rev. O. Fisher and other geologists.
According to the " planetesimal theory " of Professor T. C. Chamberlin and Dr F. R. Moulton, which assumes that the earth was formed by the accretion of vast numbers of small cosmical bodies called planetesimals, the original heat of the earth's interior was due chiefly to the compression of the growing globe by its own gravity. The heat, proceeding from the centre outwards, caused local fusion of the rocks, though without forming distinct reservoirs of molten magma, and the fused matter charged with gases rose in liquid threads or tongues, which worked their way upwards, some reaching the superficial part of the earth and escaping through fissures in the zone of fracture, thus giving rise to volcanic phenomena. It is held that the explosive activity of a volcano is due to the presence of gases which have been brought up from the interior of the earth, whilst only a small and perhaps insignificant part is played by water of superficial origin.
Entirely new views of the origin of the earth's internal heat have resulted from the discovery of radioactivity. It has been shown by the Hon. R. J. Strutt, Professor J. Joly and others that radium is present in all igneous rocks, and it is estimated that the quantity in the crust of the earth is amply sufficient to maintain its temperature. An ingenious hypothesis was enunciated by Major C. E. Dutton, who found in the radioactivity of the rocks a sufficient source of heat for the explanation of all volcanic phenomena. He believes that the development of heat arising from radioactivity may gradually bring about the local melting of the rocks so as to form large subterranean pools of magma, from which the volcanoes may be supplied. The supply is usually drawn from shallow sources, probably, according to Dutton, from a depth of not more than three or rarely four miles, and in some cases at not more than a mile from the surface. If the water in the local magma should attain sufficient expansive power, it will rupture the overlying rocks and thus give rise to a volcanic eruption. When the reservoir becomes exhausted the eruption ceases, but if more heat be generated by continued radioactivity further fusion may ensue, and in time the eruption be repeated. According, however, to Professor Joly, it is improbable that sufficient heat for the manifestation of volcanic phenomena could be developed by the local radioactivity of the rocks in the upper part of the earth's crust.

Authorities

On general vulcanicity see G. Mercalli, I Vulcani attivi della terra (1907); Sir A. Geikie, Text-Book of Geology (4th ed., 1903) (with bibliography); The Ancient Volcanoes of Great Britain (2 vols., 1897) (with general sketch of vulcanology); T. C. Chamberlin and R. D. Salisbury, Geology, Processes and their Results (1905); G. P. Scrope, Volcanoes (2nd ed., 1872); J. W. Judd, Volcanoes (2nd ed., 1881); T. G. Bonney, Volcanoes (1899); Tempest Anderson, Volcanic Studies in many Lands (1903) (excellent views). On special volcanoes see J. Phillips, Vesuvius (1869); J. L. Lobley, Mount Vesuvius (1889); H. J. Johnston-Lavis, The South Italian Volcanoes (with copious bibliography) (1891); " The Eruption of Vesuvius in April 1906," Sci. Trans. Roy. Dublin Soc. (Jan. 1909); W. Sartorius von Waltershausen, Der Aetna (herausgegeben von A. von Lasaulx, 1880); F. Fouque, Santorin et ses eruptions (1879); R. D. M. Verbeek, Krakatau (1886) (with Album Atlas); The Eruption of Krakatoa and Subsequent Phenomena, Report of the Krakatoa Committee of the Royal Society (" On the Volcanic Phenomena, &c.," by Professor J. W. Judd) (1888); Royal Society Report on the Eruption of the Soufriere, in St Vincent, in 1902, by Tempest Anderson and J. S. Flett, two parts, Phil. Trans., 1903, ser. A. vol. zoo, and 1908, vol. 208; A. Lacroix, La Montagne Pelee (1904); La Montagne Pelee apres ses eruptions, avec observations sur les eruptions du Vesuve en 1879 et en 1906 (1908); A. Heilprin, Mont Pelee (1903); E. O. Hoovey, The 1902-3 Eruptions of Mont Pelee and the Soufriere, Ninth Internat. Geolog. Congress (Vienna, 1903); Am. Jour. Sci. xiv. (1902), p. 319; Nat. Geog. Mag. xiii. (1902), p. 444; J. Milne, " The Volcanoes of Japan," Trans.' Seismological Soc. of Japan (1886); A. Stiibel, Die Vulkanberge von Ecuador (1897); I. C. Russell, Volcanoes of North America (1897); J. D. Dana, Characteristics of Volcanoes (Hawaiian Islands) (1890); C. E. Dutton, Hawaiian Volcanoes, 4th Rep. U.S. Geological Survey (1882-83), 1884; C. H. Hitchcock, Hawaii and its Volcanoes (Honolulu, 1909). For the chemistry of volcanic phenomena see F. W. Clarke, ' The Data of Geochemistry," Bull. U.S. Geolog. Survey, No. 330 (1908). For the planetesimal theory consult T. C. Chamberlin and R. D. Salisbury, Geology: Earth History, vol. ii. (1906). For other modern views of vulcanism see S. Arrhenius, Zur Physik des Vulcanismus" in Geologiska Foreningens i Stockholm Forhandlingar, Band xxii. (1900) (Abstract by R. H. Rastall in the Geological Magazine, April 1907); C. E. Dutton, " Volcanoes and Radioactivity," Journal of Geology (Chicago, 1906), vol. xiv. p. 259; G. D. Louderback, " The Relation of Radioactivity to Vulcanism," ibid. p. 747; J. Joly, Radioactivity and Geology (1909); A. Harker, The Natural History of Igneous Rocks (1909); and E. Suess, The Face of the Earth (Das Antlitz der Erde), transl. by H. B. C. Sollas, vol. iv. cap. xvi. (1909). (F. W. R.*)


Simple English

File:Mount St. Helens erupting
Mount St. Helens erupting on May 18, 1980

A volcano is a mountain where lava (hot, liquid rock) comes from a magma chamber under the ground.

Most volcanoes have a crater at the top. Materials which poured out from it usually include lava, steam, gaseous compounds of sulphur, ash and broken rock pieces.

Volcanoes erupt when magma and pressure come together, and the pressure blasts the magma out of the top. What's left is the crater.

Volcanoes are also found on planets other than Earth, like the Olympus Mons on Mars.

Contents

Types of volcanoes

The lava and pyroclastic material that comes out from volcanoes can make many different kinds of land shapes. There are three basic kinds of volcanoes.

Shield volcano

Shield volcanoes are built out of layers of basalt lava from continual eruptions (without explosions). Because the lava is so fluid, it spreads out, often over a wide area. Shield volcanoes do not grow to a great height, and the layers of lava spread out to give the volcano gently sloping sides.

Even though their sides are not very steep, shield volcanoes can be huge. Mauna Kea in Hawaii is the biggest mountain on earth. If it is measured from its base on the floor of the sea, Mauna Kea is even taller than Mount Everest, the tallest mountain on land.[1]

Cinder cone volcano

Cinder cone volcanoes are small volcanic cones that are made by pyroclastic material (the pieces of rock that come out because of an explosion) after fairly explosive eruptions.[1] The pyroclastic material makes rather steeper slopes and a narrower base than shield volcanoes. Cinder cone volcanoes usually erupt for only a short time and often are gathered together, usually on the sides of shield and composite volcanoes. They erode quickly because the pyroclastic particles are not stuck together firmly by lava.[1]

Composite volcano

Composite volcanoes, sometimes called 'stratovolcanoes', are one of the most well-known types of volcanoes. They are made by explosive eruptions of pyroclastic material, after which lava quietly pours out. Both types of eruptions make layers both of pyroclastic material and lava.[1] Composite volcanoes, like Japan's Mount Fuji, have big bases and steep sides that get steeper and steeper as it goes near the top.

How volcanoes are made

Volcanoes are usually made when two tectonic plates come together. When these two plates meet, one of them (usually the Oceanic Plate) goes under the Continental Plate. Afterwards, it melts and makes magma (inside the magma chamber), and the pressure builds up until the magma bursts through the Earth's crust.

File:Volcano

Volcano:
1. Large magma chamber
2. Bedrock
3. Conduit (pipe)
4. Base
5. Sill
6. Branch pipe
7. Layers of ash emitted by the volcano
8. Flank
9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15. Ash cloud

Other pages

Books

  • Macdonald, Gordon T., and Aiden W. O'Brien. (1970). Volcanoes in the Sea. University of Hawaii Press, Honolulu. 441 p.
  • Ollier, Cliff. (1988). Volcanoes. Basil Blackwell, Oxford, UK, ISBN 0-631-15664-X (hardback), ISBN 0-631-15977-0 (paperback).

Other websites

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References

  1. 1.0 1.1 1.2 1.3 Earth Science. Austin, Texas: Holt, Rinehart and Winston. 2001. ISBN 0-03-055667-8. 


Citable sentences

Up to date as of December 10, 2010

Here are sentences from other pages on Volcano, which are similar to those in the above article.








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