.^ 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 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.
.^ "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.
.^ 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.
Premonitory Symptoms
.^ 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.
.^ 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.
.^ 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.
.^ Yemeni officials are linking the eruption to several small earthquakes which they say hit the island on Sunday morning.
.^ 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.
.^ 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.
.^ The Volcanological Survey of Indonesia reports seismicity has increased at the volcano, and sulfuric gas was strongly smelt near Ratu Crater.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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 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.
It is probably to the uprushing current of vapour that much of
the electrical excitement which invariably accompanies an eruption
may be referred.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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
.^ 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.
.^ 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.
.^ 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.
.^ 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.
-
.^ 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.
.^ As lava flows from the Pits, a reporter vainly tries to explain the phenomena without using the terms lava or volcano.- Dante's Peak & Volano: A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]
^ 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.
.^ "It almost looks like lava," he exclaims.- Dante's Peak & Volano: A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]
^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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]
^ 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.
.^ While I was pleasantly surprised with the amount of material I found whilst viewing Dantes Peak , it is rather Volcano that inspired this piece.- Dante's Peak & Volano: A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]
^ 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.
.^ Clouds of white smoke are hanging over the area and continued earth tremors are keeping alive fears of another eruption.
.^ 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.
.^ 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.
.^ 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.
.^ 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 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.
.^ With the dam in place and reinforced by fire trucks, Jones gives the order to let the lava pool before throwing water on it.- Dante's Peak & Volano: A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [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]
^ "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.
.^ 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.
.^ 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.
.^ 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]
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°.
.^ So, if the tunnel is collapsed anywhere, even partially, wouldnt that just cause the lava to break through at that point?- Dante's Peak & Volano: A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]
.^ 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.- Dante's Peak & Volano: A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]
^ 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 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]
The wallrock thus dissolved in the magma will not be
without influence on the composition of the lava with which it
becomes assimilated.
.^ 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 (!- Dante's Peak & Volano: A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]
.^ 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]
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.
.^ "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.
.^ 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.
.^ 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]
^ Heche, meanwhile, suggests dumping water on the trapped lava to form a crust, which will help in damming it up.- Dante's Peak & Volano: A Jabootu Nugget 28 January 2010 1:01 UTC www.jabootu.com [Source type: General]
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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ Kelud volcanic lake is one of the most active and most dangerous stratovolcano in Indonesia.
.^ 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.
.^ 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.
.^ Current geological theory states that prediction is impossible (or close to it) due to the nature of sudden fracture (brittle fracture theory).
.^ 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.
.^ "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."
.^ 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.
.^ 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.
.^ 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.
.^ 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
|
|
|
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.
.^ 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.
.^ 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.
.^ 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 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.
.^ 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.
.^ 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.
.^ "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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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 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 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
.^ 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.
.^ "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.
.^ 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.
.^ 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 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.
.^ 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.
.^ No eruption has occurred yet, but seismic activity has commenced.
.^ 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.
.^ Another surprise was that he found fewer volcanoes on the seabed around Hawaii, another volcanic hotspot.
.^ 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 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.
.^ 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.
.^ 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.
.^ Volcanic activity generates harmonic scalar resonance precursors.
The effect of the contact of lava with water is often
misunderstood.
.^ 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.
.^ 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.
.^ 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.
.^ 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 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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. -
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ "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. - . 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.
.^ 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.
.^ 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.
.^ 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 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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°.
.^ 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 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.
.^ 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.
.^ 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.
.^ 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 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!
.^ 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°.
.^ 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.
.^ 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 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.
.^ 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, 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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 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.
.^ 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. -
. 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.
.^ 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.
.^ 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.
.^ 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.
.^ 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.*)
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