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Natural Disasters. Volcanoes: Types and Eruption Styles. Magma Review. Basalt. Andesite. Rhyolite. Types of Volcanoes. Basaltic Volcanoes Shield volcanoes Cinder cones Andesitic Volcanoes stratovolcanoes Rhyolitic Volcanoes Lava domes calderas. Basaltic Volcanoes. Shield Volcanoes
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Natural Disasters Volcanoes: Types and Eruption Styles
Magma Review Basalt Andesite Rhyolite
Types of Volcanoes Basaltic Volcanoes Shield volcanoes Cinder cones Andesitic Volcanoes stratovolcanoes Rhyolitic Volcanoes Lava domes calderas
Basaltic Volcanoes Shield Volcanoes • Large, broad gentle slopes – resembles a “warrior’s shield” • Fluid basalt able to travel great distance • Low volatile (gas) content – generally non-explosive
Shield Examples Hawaiian Islands • “Big Island” – Mauna Loa, Kilauea, and Mauna Kea Mauna Loa (largest volcano)
Basaltic volcanoes Cinder Cones • Small size, steep slope • Erupt when magma encounters groundwater • Single eruptive period (months to few years) • Built up by loose cinders around small crater
Cinder Cone Examples Cima Volcanic Field Red Hill Amboy Crater California Cinder Cones
Andesitic Volcanoes Stratovolcanoes • Alternating layers of lava, debris, and ash • Moderate volume and size • Moderate to high volatile content • Violently explosive • Erupts repeatedly
Stratovolcano Examples Cascade Ranges Mt. Hood Mt. Rainier Mt. Lassen
Rhyolitic Volcanoes Lava Domes • Rough dome with many spines • Very high viscosity – magma does not travel far • Low volatile (gas) content
Lava Domes Examples Central California Mono Craters Wilson Butte Panum Crater
Rhyolitic Volcanoes Giant Continental Calderas • Circular, enclosed depressions • Typically filled with water to form lakes • Result from collapse volcanic structure • Due to underlying emptying of magma
Continental Caldera Example Yellowstone National Park Crater Lake, Oregon
Explosive Eruption Styles Hawaiian Phreatomagmatic Strombolian Vulcanian Pelean Plinian
Hawaiian • Low-viscosity, fluid basalt • Non-explosive
Phreatic & Phreatomagmatic • Hot magma comes in contact with shallow groundwater • Water heats up and erupts steam, rock fragments, and magma • Violently explosive • Phreatic = no new magma on surface
Strombolian • Distinct blasts of magma • Produce incandescent bombs • Small tephra cone results • Mildly explosive
Vulcanian • Sustained eruption of rock or viscous magma to several km • Collapse to produce pyroclastic flow • Widespread tephra fall • Very explosive
Pelean • Collapse of lava dome • Produce glowing avalanches (nuée ardentes) • Violently explosive
Plinian • Sustained eruption columns up to 45 km • Produce widespread ash deposits • Collapse of column to pyroclastic flow • Violently explosive
Eruption Warning: Volcanic Precursors • Active Volcano • Has shown activity in recorded history • Extinct Volcano • Has not shown any historic activity • Dormant Volcano • Has not shown activity in recorded history but shows evidence of activity in geologic past
Long-Term Forecasting • Ancient studies help scientist assess hazards and risk posed by future volcanoes
Short-Term Forecasting • Seismic waves • Magnetic field changes • Electrical Resistivity • Ground Deformation • Changes in groundwater • heat flow • Gas composition