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Volcanos (Mount St. Helens (May 18 (5.1 earthquake, Northern bulge slide…
Volcanos
Mount St. Helens
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March 16, first activity, 100 earthquakes
March 24, 20 earthquakes an hour
April 1, plumes of steam and ash read 200,000 feet in air
April 22, eruptions occur on average about 1 per hour
April 29, State official closed area around the volcano, evacuates people from RED ZONE
May 7-17, small eruptions, north side of volcano bulged
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How much Damage
57 deaths, only 3 in Red Zone
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Volcanic Eruptions
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Dissolved Gases
When dissolved gases are in the presence of magma it can contributes to how explosive a volcano can be
Lava Flows
Lava flow is the magma from below volcanoes that come out of the volcano and move very slow and are rarely deadly
Ash Fall
During a very explosive eruption, volcanoes can erupt very large amounts of ash into the air
Mudflows
Sometimes, when a volcano erupts, they can cause mudflows by the thermal heat they give off and melting the snow and ice to mix with the mud or ash around it to create mudflows
Pyroclastic Flow
Explosive volcanoes and make large avalanches fo hot gas, ash, and rock, creating an pyroclastic flow
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Types of Volcanoes
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Composite Volvano
Large steep-sided volcanoes that result from explosive eruptions of andesitic and rhyolitic lava and ash along convergent plate boundaries
Cinder Cone Volcanoes
Small steep-sided volcanoes that erupt gas-rich, basaltic lavas
Caldera Volcanoes
Large volcanic depression formed when a volcano's summit collapses or is blown away by explosive activity
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How do volcanoes form
Volcanoes can form large mountains, new crust, and leave a path of destruction behind.
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Boundaries
Convergent
Subduction zones, magma is less dense than the plates
Divergent
Plates separate, magma rises
Hot spots
Not a plate boundary, convection zone
Types of Eruptions
Quit
Pours out, runs down the side
Explosive
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High viscous lava, pressure releases at weak point (crater)
ash, rock, pyroclastic flow
Pahoehoe
fast moving, low viscosity
AA
slow moving, high viscosity
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What is a volcano
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Then what is in the volcanoes is magma, rock that is below the Earth's surface
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Where do volcanoes form
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The Ring of Fire is called this because it is an area of earthquakes and volcanoes surrounding the Pacific Ocean
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Beliefs
Pompeii
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Population estimated 11,000
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Annual festival - held August 23, one day before the eruption
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