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Published byVictoria Griffith Modified over 9 years ago
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Volcanoes
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l Evidence that we live in an active planet l The gods of the underworld l Millions of people live near active volcanoes –The greatest geological hazard
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Mount Saint Helens- after
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Hazard
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Future hazard l Population near big, recently active volcanoes –Seattle –Mexico City –Quito –Indonesia –Japan
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Lava l Molten rock that flows on the surface l Basaltic Lava –low silica, –fluid, –low gas, –not explosive l Andesitic Lava –high silica –viscous –gas-rich –explosive
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Types of volcanoes l 1. Shield Volcanoes –Hawaii, Iceland –Basaltic l 2. Stratovolcanoes (or composite) –Mt. Saint Helens, Pinatubo, etc –Andesitic –Explosive
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Shield Volcanoes l Huge broad cones l Gentle slopes l Made from lava flows l Basaltic l Form at hotspots l Not very dangerous l Predictable
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Stratovolcanoes (composite) l Andesitic lava l Rich in dissolved gases l Violent eruptions alternate with lava flows l Steep-sided cones l Very dangerous l Unpredictable
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Pyroclastic Flows l Product of explosive eruptions l Hot ash shot up into the atmosphere l Ash column collapses l Pyroclastic flow can travel 60 mi/hr l Ash can fall 100’s of miles away l Ash may affect global climate
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Mt. Saint Helens before
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Phreatic (vapor) eruption
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Bulge
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Mt. St. Helens Pyroclastic Eruption
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After the eruption
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Lahars (mudflows)
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l Very destructive l Kill as many people as the eruption itself l Loose ash forms mud avalanches l Glaciers on top of volcano melt l Rain
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Inside a volcanoe
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Pyroclastic eruption
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Volcanic landscape: A Caldera (Crater Lake)
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Crater lake formation (caldera) l 1. Early eruptions from composite cone l 2. Great eruption empties the magma chamber l 3. Summit collapses l 4. Caldera fills with water
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Plate Tectonic Settings of Volcanism
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Plate tectonic settings of volcanoes
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