Volcanic Activity

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Volcanic Activity
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How Magma Reaches Earths Surface

• Lava Begins as magma in the (asthenosphere)
  mantle.
• Magma is less dense than solid material so it
  rises toward the surface.
• When a volcano erupts, dissolved gases form
  bubbles that rush out, taking the magma with
  them. Like opening a can of soda pop.

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Inside a Volcano

• Pipe a long tube in the ground that connects the
  chamber to the Earths surface.
• Vent where magma, and gas leave the volcano.
• Lava flow the river of lava that comes out and
  over the land.
• Lava Magma that reaches the surface is called
  lava.
• Crater a bowl-shaped area that forms around the
  vent.
• Magma chamber collects in pockets beneath the
  volcano.

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Characteristics of Magma

• The force of an eruption depends on four things
• Amount of gas in magma
• How thick or thin the magma is
• Its temperature
• Silica content
• Silica also determines how easily the magma
  flows.
• More silica thicker and lighter colored lava
  sticky
• Makes obsidian and Rhyolite and pumice
• Less Silica darker colored lava flows easily
• Makes basalt

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Types of Volcanic Eruptions

• Quiet Eruptions
• Magma is thin and flows easily
• Pahoehoe is a fast-moving hot lava, mass of
  wrinkles, billows and ropelike coils when it
  hardens.
• AA is a slow moving cool lava, rough and jagged
  when it hardens
• Explosive Eruptions- thick magma, pipe gets
  plugged and explodes when pressure builds up.
• Causes pyroclastic flow explosive eruption hurls
  out gas, ash (sand-like), cinders (pebble sized),
  and bombs (larger pieces, ranging from baseball
  to car sized).

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Stages of a Volcano

• Active or live volcano that is erupting or shows
  signs that it erupt in the near future.
• Dormant or sleeping scientists expect the
  volcano to erupt in the future and become
  active.
• Extinct or dead is unlikely to erupt again.

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Volcanic Landforms
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Landforms from Lava Ash

• Shield Volcanoes
• Cinder Cone Volcanoes
• Composite Volcanoes
• Lava Plateaus
• Calderas

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Shield Volcanoes

• Thin layers of lava pour out of a vent and harden
  on top of previous layers.
• Build a wide, gently sloping mountain.
• Hawaiian Islands are shield volcanoes over a hot
  spot.

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Mauna Loa, Hawaii
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Cinder Cone Volcanoes

• A steep, cone-shaped hill or mountain.
• Ash, cinders, and bombs pile up around the vent.
• Cinders erupt explosively.
• Sunset crater is an example.

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Cinder Cone Volcanoes

• A steep, cone-shaped hill or mountain.
• Ash, cinders, and bombs pile up around the vent.
• Cinders erupt explosively.
• Sunset crater is an example.

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Lava Plateaus

• Continued eruptions form high, level areas.
• Lava flows out of several long cracks, and after
  millions of years, these layers form high
  plateaus.
• Example Columbia Plateau

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Columbia Plateau
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Calderas

• A huge eruption may empty the main vent and the
  magma chamber beneath the volcano.
• Mountain becomes a hollow shell and the top
  collapses in.
• Huge hole left is called a caldera.
• Example Crater Lake, Oregon

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• Poas Volcano,
• Costa Rica
• Crater Lake,
• Oregon