Chapter7_post - Volcanoes: Hazards and Mitigation Volcanic...

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Volcanoes: Hazards and Mitigation Volcanic Hazards Pyroclastic flows and surges Volcanic mudflows (lahars) Ash and pumice falls Poisonous gases Lava flows Predicting eruptions Understand the historic volcanic record Volcanic precursor events (eruption warnings) and monitoring these events Mitigation of Damage Populations at Risk Italy American Pacific Northwest (the Cascade Range) Yellowstone hot spot
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Volcanic Hazards Most lives are taken by Pyroclastic flows Lahar (mudslides) Tsunami Other volcanic hazards Ash falls Poisonous gas Lava flows Landslides
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Pyroclastic Flows Mixture of very hot rock fragments, ash and gases/steam that flow downhill away from vent, at very high speed, close to ground surface http://digg.com/general_sciences/Incredible_video_of_pyroclastic_flow
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How do pyroclastic flows start? 1. Landslide 2. Dome collapse 3. Eruption column collapse
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Pyroclastic Flow: Mount Unzen 6/3/1991 Induced by landslide 3 volcanologists and 40 journalists were killed.
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lava dome on 5/22/93 pyroclastic flow on 6/24/1993 lava dome on 2/16/1995 Pyroclastic Flow: Mount Unzen, Japan Induced by lava dome collapse New dome
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Pyroclastic Flow: Mont Pelée, Martinique 1902 First record of an active pyroclastic flow Temperature >700 o C; Speed ~190 km/hr ~30,000 people killed; city completely destroyed St. Pierre: “ Paris of the Caribbean
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Pyroclastic Flow: Mont Pelée, Martinique 1902
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Pyroclastic Flow: Mount St. Helens 15 s 30 s 1 min 5 min 7/22/1980
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Pyroclastic Flows and Surges Ash- and steam- rich, shock wave surge may race ahead of pyroclastic flow, up to 600 km/hr Surge associated with the directed blast of the May 1980 Mt. St. Helens eruption stripped and flattened trees along its path.
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Pyroclastic Flows: Movement Over Water During eruption of Vesuvius in 79, glowing pyroclastic flow crossed some 30 km of the Bay of Naples. In 1883, 2000 people died in hot ash flows that crossed >40 km of open sea in SE Sumatra during the Krakatau eruption. In 1902, pyroclastic flows from Mount Pelée burned boats and ships anchored in the harbor.
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Pyroclastic Surge: Movement Over Water During eruption of Vesuvius in 79, glowing pyroclastic flow crossed some 30 km of the Bay of Naples. In 1883, 2000 people died in hot ash flows that croseed >40 km of open sea in SE Sumatra during the Krakatau eruption. In 1902, pyroclastic flows from Mount Pelée burned boats and ships anchored in the harbor. Pyroclastic surge (ash- and steam-rich cloud) moving over Sea Montserrat, 1996
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Volcanic Mudflows (“lahars”) • As steam that has been blown up into atmosphere spreads out, it cools and condenses heavy rain thick volcanic mudflows ( lahars ) • Lahars can also without volcanic rain--from normal rain or from melting of glacier or ice on volcano
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Chapter7_post - Volcanoes: Hazards and Mitigation Volcanic...

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