What is a Volcano?

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What is a Volcano?

• Volcano-A weak spot in the crust where molten
  material comes to the surface.

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Volcano locations

• Ring of fire-Major volcanic belt around the
  Pacific Ocean. (plate boundary)

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Island Arc-A ring of islands that forms over a
plate boundary.
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Hot spot-An area where a volcano forms in the
middle of a continental or oceanic plate when
magma melts through the crust like a blowtorch.
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Types of Volcanoes

• Composite explosive eruptions that release huge
  amounts of gas and ash. pyroclastic flows and
  lahars can occur. Can produce dust bombs and
  blocks. This type is found on continental-oceanic
  plate boundaries. (ie. Mt. Rainer, Mt. St.
  Helens, Mt. Hood)

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Shield mainly lava flows (ie. Mt. Kilauea)
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Cinder Cone bombs, ash, and cinder are ejected
from a volcanic vent and produce a cone.. (ie
Sunset Crater, Arizona)
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Types of Eruptions

• Type of eruption is determined by the type of
  magma in the volcano
• Quiet Eruptions basaltic-thin, runny lava.

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Explosive Eruptions

• granitic-thick, sticky lava. (It gets stuck,
  pressure is built, and it explodes)

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Activity of Volcanoes

• Active is erupting or has shown signs that it
  may erupt in the near future.

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Dormant is sleeping, but scientists expect it
to awaken in the future.
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Extinct unlikely to erupt again.
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Structure of a Volcano

• Magma-Extremely hot molten material that also
  includes dissolved gases and including water
  vapor.
• Magma Chamber-A large underground pocket formed
  as magma rises toward the surface.

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• Pipe-A narrow almost vertical crack in the crust
  through which magma rises to the surface.
• Vent-Point on the surface where magma leaves the
  volcanos pipe.

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• Side Vent-When magma forces its way out a volcano
  through the side.
• Crater-A bowl shaped area that forms around the
  volcanos vent.

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• Lava-Magma that reaches the surface.
• Lava Flow-The river of lava that pours down a
  volcano and over the land.

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What comes out of a volcano?

• Gases-Carbon Dioxide and Sulfur Dioxide are
  common gases. Steam also comes out.

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Lava-What magma is called when it reaches the
Earths surface and loses some of its gas.
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• Aa-Cool, slow moving lava.

• Pahoehoe-Hot, fast moving lava.

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Blocks-Have sharp corners, are chunks of rock
blown out from inside the volcano.
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Bombs-Masses of lava that cool into rounded
shapes before hitting the ground.
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Cinder-When lava is blown into the air during an
eruption, it sometimes cools into small, rough
pieces of rock that are puffed up by gas.
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Pumice-Formed like cinder, but contains more
trapped gas. Light enough to float on water.
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Ash-Lava that has been blown apart by gases into
sand-like particles.Dust-The smallest particles
of ash
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Tuff-When ash mixes with rain or other moisture
and forms a hard, cement-like rock.
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Lahar-A hot or cold mixture of water and rock
fragments flowing down the slopes of a volcano or
river valley.
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Pyroclastic Flow-A high density cloud that is
mixture of hot, dry rock fragments and gas moving
away from the vent at high speeds. Temperature
is between 200?C to 700?C.
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Volcanic Landforms

• Dome Mtn. magma is trapped below a horizontal
  layer and pushes it into a dome shape and cools.

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Sill magma cools horizontally between rock
layers
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Dike magma cools vertically btwn. rock layers
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Volcanic Neck - formed when magma cools in a
volcanic pipe.
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Lava plateau high level area formed by thin,
running lava.
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Batholith mass of rock formed when a large mass
of magma cools below the surface.
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Caldera huge hole left by the collapse of a
huge volcano.
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Volcanoes in Space

• Mars-Has the largest volcano called Olympus Mons.
  Around the base of the volcano is a cliff that
  equals 5 times the size of the Grand Canyon.

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Volcanoes in SpaceVenusHas the most volcanoes
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Moon

• Craters are NOT from volcanoes. They are from
  meteorites smashing into the moon. Lava flows
  more than 3 billion years ago created smooth dark
  areas on the moon.

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THE END????
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Sept 2006
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14 October 2004
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http//vulcan.wr.usgs.gov/Outreach/AboutVolcanoes/
framework.html