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Volcanoes. 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.

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Presentation on theme: "Volcanoes. 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."— Presentation transcript:

1 Volcanoes

2 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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4 Mount Saint Helens- after

5 Hazard

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7 Future hazard l Population near big, recently active volcanoes –Seattle –Mexico City –Quito –Indonesia –Japan

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10 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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13 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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15 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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22 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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25 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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28 Mt. Saint Helens before

29 Phreatic (vapor) eruption

30 Bulge

31 Mt. St. Helens Pyroclastic Eruption

32 After the eruption

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34 Lahars (mudflows)

35 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

36 Inside a volcanoe

37 Pyroclastic eruption

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39 Volcanic landscape: A Caldera (Crater Lake)

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41 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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44 Plate Tectonic Settings of Volcanism

45 Plate tectonic settings of volcanoes


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