Igneous Activity

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Igneous Activity
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The Nature of Volcanic Eruptions

• Factors that determine whether a volcano erupts
  explosively or gently
• Magmas composition
• Temperature
• Dissolved gases
• These factors affect viscosity
• Higher silica contenthigher viscosity
• Higher temperaturelower viscosity
• Gases provide force

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The Nature of Volcanic Eruptions

• Three kinds of magma
• Basaltic50 silica, least viscous, tendency to
  form lavas, high melting temperature
• Andesitic60 silica, intermediate on all
  properties
• Granite70 silica, most viscous, tendency to
  form pyroclastics, low melting temperature

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What is Extruded During Eruptions?

• Lava Flows
• Pahoehoeropy basaltic lava flows
• Aabasaltic lava flow that leaves sharp edges

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What is Extruded During Eruptions?

• Gases
• 1-5 of the total weight of magma
• 70 water vapor
• 15 carbon dioxide
• 5 nitrogen
• 5 sulfur
• Chlorine, hydrogen, and argon
• Natural source of air pollution

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What is Extruded During Eruptions?

• Pyroclastics (fire fragments)
• Fine ash particles (contain lots of gas)
• Welded tuffash shards fused together
• Pumicelarger pieces of welded tuff
• Cinderspea sized
• Lapilli (little stones)walnut-sized
• Blocksparticles larger than lapilli
• Bombsejected as incandescent lava

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Volcano Types

• Shield
• Broad, slightly domed structure
• Primarily basaltic lava flows, only a small
  percentage of pyroclastic material
• Mauna Loalargest
• Kilaueaactive today

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Volcano Types

• Cinder Cones
• Built from ejected lava fragments
• Steep angle
• Rather small
• Paricutin, Mexico

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Volcano Types

• Composite Cones (Stratovolcano)
• Most in the Ring of Fire
• Large, nearly symmetrical
• Formed from relatively viscous andesitic lavas
• Can suddenly change eruptive style to pyroclastic
  flows
• Mt. Fuji
• Mt. Vesuvius

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Volcano Types

• Composite Cones (cont.)
• Nuee ardente
• Fiery cloud that can race up to 125 miles per
  hour
• Lahars
• Mudflowash and debris combine with water

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Other Volcanic Landforms

• Calderas
• Crater that exceeds one kilometer in diameter
• Most are formed following explosive eruptions
• They form when the summit of a volcano collapses
  into the partially emptied magma chamber below
• Crater Lake in Oregon
• Vents
• Pipelike pathway from a magma chamber to a crater

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Other Volcanic Landforms

• Volcanic neckwhen most of a cinder cone erodes,
  leaving the rock that occupies the vent
• Fissurefractures in the crust that pour forth
  lava
• Lava plateausflood basalts that come from
  fissures and cover extensive areas
• Pyroclastic flowscome from vents at high speeds
  and blanket extensive areas