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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.
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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.
Types of Volcanoes Volcanoes are the product of the tectonic activity underneath Earth’s crust as a result of convection in the mantle. They are found especially at subduction zones, hot spots, and divergent mid-ocean ridges.
Types of Volcanoes VOLCANO 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 Extinct – Some volcanologists don’t use this term; the volcano is supposedly no longer active and may be unable to become active.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.
Shield Volcano Non-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.
Cinder Cone Volcano Non-explosive eruptions of basaltic 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.
Composite or Stratovolcano Explosive andesitic viscous magma rich in silica that is layered with lava and rock from old eruptions. Periods of inactivity followed by huge, violent explosions. Examples: Mt. Rainier in Washington and Mt. Fuji in Japan
Mid-Ocean Ridge/Underwater Pillow lavas above, Black smoker at mid-ocean ridge, & Iceland erupts Divergent boundary produces usually fluid basaltic magma. Large rifts may erupt volumes of lava. Underwater pillow lavas may form.
Basaltic Lava Types Pahoehoe is “smoother” lava at the surface, while A’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
Volcanic Products Geologic 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!
Projectile Volcanic Products Ash, tephra, lava bombs, lapilli, pele’s tears, cinder, pumice, and other volcanic products may be ejected through the air.
Other Volcanic Hazards Pyroclastic 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.
