A1262045711rnLbK

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SUBAQUEOUS ERUPTIONS
Submarine eruptions Quiet and effusive. May
produce submarine shield volcanoes. If deep
enough, water pressure prevents
gas escape. Produces pillow structures. Shallo
w eruptions can be explosive. Contact of water
with hot magma produces lots of steam and
consequently tephra.
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SUBGLACIAL ERUPTIONS
Mafic lava erupts under glaciers. Causes rapid
melting of snow and ice. Large amounts of
meltwater is freed. Bardabunga and Grimvötn
volcanoes erupted under Vatnajökull on Iceland
in 1996. Outburst flood occurred. Termed
JOKULHLAUP.
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JOKULHLAUP
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PYROCLASTIC ERUPTIONS
Involve viscous, gas-rich magmas. Produce large
amounts of tephra. Area receives large amounts of
hot ash, nuée ardente, and hot lahars.
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Mt. Vesuvius Herculaneum, Italy, 79 A.D.
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With little gas or water felsic magmas will
produce a VOLCANIC DOME in the crater. If
pressure is not released, massive eruptions
occur. Produces CALDERA. Mt. Mazama,
OR Krakatau, Indonesia Mt. Desert Island, ME Mt.
St. Helens, WA
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Mt. St. Helens, WA
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Crater Lake and Wizard Island (Mt. Mazama), OR
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PYROCLASTIC VOLCANIC CONES
Structure and shape depends on magma
type. Intermediate and felsic volcanoes produces
large amounts of tephra. Tephra generally
accumulates close to vent. Forms steep-sided
cinder piles. The cinders are covered with the
next lava flow event. Process repeats. Produces
COMPOSITE or STRATOVOLCANO. Possesses alternating
layers of lava and pyroclastics. Mt. Hood, OR ,
Mt. Ranier, WA, Mt. Shasta, CA
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PYROCLASTIC VOLCANIC CONES
COMPOSITE or STRATOVOLCANO
Mt. Hood, OR
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PYROCLASTIC CONES or CINDER CONES
Composed entirely of volcanic cinders. Generally
small volcanoes lt1000 m (3000) in height. Have
steep sides. No intervening lava between
cinders. Easily eroded. Can form from any type of
magma as long as enough gas exists to keep
blowing particles up into the atmosphere. Sunset
Crater, AZ and Paricutin, Mexico
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PYROCLASTIC CONES or CINDER CONES
Sunset Crater, AZ
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PYROCLASTIC CONES or CINDER CONES
Paricutin, Mexico
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Volcano Explosivity Index (VEI)