Volcanic Activity

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Volcanic Activity
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How Magma Reaches the Surface

• Magma forms 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)
• the magma with them. Like When a volcano Reaches
  Earths Surface

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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

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

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Volcanic Landforms
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Landforms from Lava Ash

• A. Shield Volcanoes
• B. Cinder Cone Volcanoes
• C. Composite Volcanoes
• D. Lava Plateaus
• E. 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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Composite Volcanoes

• A steep, cone-shaped volcano built up of layers
  and of rock fragments.
• Steep at the top, flatens at the bottom
• Magma- high in silica, making it pasty.
• Erupt explosively.
• Mount St. Helens and Mount Rainier are examples.

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• St. Augustine volcano, Alaska.

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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

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Volcano Hazards

• Mount St. Helens erupted in 1980 after 123 years
  of being dormant. Before that people viewed it
  as a peaceful mountain.
• Quiet eruption hazards- lava flows from vents,
  burning everything in their path.
• Explosive eruption hazards- volcano will send out
  burning clouds of volcanic gases, cinders and
  bombs.
• Volcanic ash can bury entire towns, damage crops
  and clog car engines. Wet ash can cause roofs to
  collapse and plane engines to stall.