volcanoes
DESCRIPTION
Volcanoes. An overview of volcano types, products, and hazards SD’11. Types of Volcanoes. A volcano is a vent in the earth's crust through which lava, steam, ashes, etc., are expelled, either continuously or at irregular intervals. Volcanoes may be huge mountains or small cracks and fissures. - PowerPoint PPT PresentationTRANSCRIPT
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Volcanoes
An overview of volcano types, products, and hazards
SD’11
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Types of VolcanoesA volcano is a vent in the
earth's crust through which lava, steam, ashes, etc., are expelled, either continuously
or at irregular intervals.
Volcanoes may be huge mountains or small cracks
and fissures.
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Types of VolcanoesVolcanoes are the product of the tectonic activity underneath Earth’s crust as a result of convection in the mantle.
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They are found especially at subduction zones, hot spots, and divergent mid-ocean ridges.
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Types of VolcanoesVOLCANO TYPE VOCABULARY:
Active – The volcano is in a “current” eruption cycle.
Dormant – The volcano is “sleeping,” but may become active.
Extinct – Some volcanologists don’t use this term; the volcano is supposedly no longer
active and may be unable to become active.
Explosive -- Magma is more viscous and therefore retains the build-up of pressure
until the volcano erupts explosively. Usually a major hazard to those
around it when erupting…especially andesitic magma like on continents.
Non-explosive -- Magma is less viscous and allows gases to escape easier. Fluid
magma is possibly less of a hazard to those around it when erupting…
especially basaltic magma like hot spots or divergent mid-ocean ridges.
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Shield VolcanoNon-explosive eruptions of dark, fluid,
basaltic magma high in Fe and Mg. Low viscosity of the magma allows for the
flow off the mountain making the shield shape.
Example: Mauna Kea, Mauna Loa, Hualalai, and Kilauea which make up the “big island” of Hawaii.
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Cinder Cone VolcanoNon-explosive eruptions ofbasaltic magma high in iron.Produces tephra (ash, dust,
rocks, & lava bombs). Steep sided with a conical
shape. Very common type of volcano.
Example: Paricutin, Mexico. This volcano erupted in a field in 1943.
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Composite or StratovolcanoExplosive andesitic viscous magma rich in
silica that is layered with lava and rock from old eruptions.
Periods of inactivity followed by huge, violent explosions.
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Examples: Mt. Rainier in Washington and Mt. Fuji in Japan
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Some Volcanic Rock Formations
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Mid-Ocean Ridge/Underwater
Divergent boundary produces usually fluid basaltic magma. Large rifts may erupt volumes of lava. Underwater pillow lavas may form.
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Pillow lavas above,
Black smoker at mid-ocean ridge, &
Iceland erupts
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Basaltic Lava Types
Pahoehoe is “smoother” lava at the surface, whileA’a lava is a rougher more viscous rocky lava that
crumbles as it flows.
A sampling of Hawaiian lava A’a crumbles over an older
pahoehoe flow
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Volcanic ProductsGeologic products
include many types of igneous rock.
Also many formations that are volcanic in origin such as Devil’s Tower in Wyoming & Morro Rock in Morro Bay!
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Projectile Volcanic Products
Ash, tephra, lava bombs, lapilli, pele’s tears, cinder, pumice, and other volcanic products may be ejected through the air.
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Other Volcanic HazardsPyroclastic flows of
HOT ash, rock, and debris move quickly down the slope.
Lahars are mud flows from either rains after eruptions or flash melted snow/glaciers that carry ash and debris.
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Other hazards to considerQuickTime™ and a
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The End!