Volcanism

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Volcanism

• Volcanic Features  
• Location and Types of Volcanic Activity  
• Effusive Eruptions  
• Explosive Eruptions  
• Volcano Forecasting and Planning

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Volcanic Settings
Figure 12.24
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Shield and Composite Volcanoes
Figure 12.32
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EFFUSIVE ERUPTIONS

• Generally at hots spots, spreading centers
• Mantly comes directly to surface
• Hot lava low viscosity, very mafic, flows
  easily, gases escape easily
• Forms shields, flood basalts

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FLOOD BASALTS
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Composite Volcano
Columbia River basalt flow
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EXPLOSIVE ERUPTIONS

• Found at subduction zones
• Magma low temp (800 degrees C), high viscosity,
  does not flow easilty, more felsic mineralogy,
  gases trapped, hard to predict explosions
• Forms composite volcanoes, cinder cones,
  calderas, aerial bombs, nuee ardente gas flows,
  very destructive

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Composite Volcanoes
Figure 12.34
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Nuee ardente pyroclastic flow, of searing
superheated gas and incandescent volcanic ash and
dust
Mount Pelee, on the Carribean island of
Martinique, 1902 eruption. All but 2 of the more
than 20,000 people in the town of St. Pierre were
killed.
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KRAKATAU Worlds largest explosion?
Over a century ago, on August 26,1883, the island
volcano of Krakatau ("Krakatoa") in Indonesia, a
virtually unknown volcanic island with a history
of violent volcanic activity, exploded with
devastating fury. The eruption was one of the
most catastrophic natural disasters in recorded
history. The effects were experienced on a
global scale. Fine ashes from the eruption were
carried by upper level winds as far away as New
York City. The explosion was heard more than 3000
miles away. Volcanic dust blew into the upper
atmosphere affecting incoming solar radiation and
the earth's weather for several years. A series
of large tsunami waves generated by the main
explosion, some reaching a height of nearly 40
meters (more than 120 feet) above sea level,
killed more than 36,000 people in the coastal
towns and villages along the Sunda Strait on Java
and Sumatra islands. Tsunami waves were recorded
or observed throughout the Indian Ocean, the
Pacific Ocean, the American West Coast, South
America, and even as far away as the English
Channel.