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From Wikipedia, the free encyclopedia

Volcanism is the phenomena connected with volcanoes and volcanic activity. It brings magma from the mantle within a planet and rises to the surface as a volcanic eruption.[1] In some cases, rising magma can cool and solidify without reaching the surface of a planet. Instead, the cooled and solidified igneous mass freezes within the crust of a planet to form an igneous intrusion. Intrusions can be in the form of batholiths, dikes, sills and layered intrusions.

See also



Up to date as of January 23, 2010
(Redirected to Volcanoes/Volcanism article)

From Wikibooks, the open-content textbooks collection

< Volcanoes


There are three (3) major types of lavas formed by volcanoes. Mafic, Intermediate, and Felsic.

  • %SiO2: < 50%
  • %FeMg: 4%
  • Temp: up to 1500C
  • Viscosity: Low
  • Eruptive Behavior: gentle
  • Distribution: divergent plate boundries, hot spots, convergent plate boundries


  • %SiO2: ~60%
  • %FeMg: ~3%
  • Temp: ~1000C
  • Viscosity: Intermediate
  • Eruptive Behavior: explosive
  • Distribution: convergent plate boundries


  • %SiO2: >70%
  • %FeMg: 2%
  • Temp: 700C
  • Viscosity: High
  • Eruptive Behavior: explosive
  • Distribution: hot spots in continental crusts (Yellowstone National Park)

An interesting exception to this classification is the carbonitite volcanoes. These volcanoes have a significant amount of calcium/magnesium carbonates in their magma. While low in Silica and with a low viscosity, which would place these lavas in the mafic class, they are also low in iron and vary in their magnesium. The origin of the CO (typically CO3) in these magmas is a geologic puzzle at present. Is it present in the original magma coming up from the mantle or has it been incorporated by the melting of rocks that the magma has passsed through? Solving this puzzle is made harder since there is only one volcano known to have carbonitite lava eruptions in recent times, Ol Doinyo Lengai in the East African Rift Valley. This volcano has a gentle eruptive behavior today but in the past has been explosive. The fossil footprints of Laetoli, Kenya (showing bipedal hominids existing 3.7 million years ago) are preserved in a carbonitite ashfall.

An interesting, though very technical, article showing how geologists are using chemistry to try to determine the origins of carbonitite magmas is at [1]

Simple English

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