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Volcanoes (Mount St. Helens ("coughing mountain", 1792 - British…
Volcanoes
Mount St. Helens
"coughing mountain", 1792 - British explorer named it "Baron St. Helens" after his best friend
March 16 - first activity, 1,000 earthquakes in one week
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May 18 - 5.1 earthquake at 8:30 am, northern bulge, ash rises up to 15 miles, lateral eruptions to 20 miles, pyroclastic flows
57 deaths, on in the red zone, thousands of animals, 200 homes destroyed, 185 miles of road/15 miles of railroad
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What is a volcano?
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pahoehoe - smoot, shiny surfface
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Volcanic Eruptions
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Gases - water vapor, carbon dioxide, sulfur oxide
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pahoehoe - fast moving, low viscosity
aa - slow moving, high viscosity
Explosive - start with vent blocked, high viscous lava, pressure resales at weak point (crater)
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Parts of Volcanoes
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Pipe - leading from under ground to the vent, the tube inside the volcano, moves the magma
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Beliefs around Volcanoes
Scarifies - rabbits, fish, small animals
Annual festival, August 23
Gods and Goddess, Vulcan - God of fire
POMEII - vacation for wealthy Romans, 11,000 people, Advanced complex system
Frequent earthquakes, few buildings were repaired
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Mount Vesuvius - erupted in August 24, 79 A.D.
How do volcanoes form?
Scientists have learned that the movement of Earth's tectonic plates causes the formation of volcanoes and the eruptions that result
Convergent plate boundaries - volcanoes can form along convergent plate boundaries, subduction zones, magma is less dense than the plates, rises through the cracks
Divergent plate boundaries - lava erupts along divergent plate boundaries, plates separate magma rises that the vent or opening created
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Hot spots - volcanoes that are not associated with plate boundaries, rising convection current (plume)
Where do volcanoes form?
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In more populated areas, the USGS has developed a hazard assessment program
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Types of Volcanoes
Composite volcanoes - large, steep-sided volcanoes that result from explosive eruptions of andesitic and rhyolitic lava and ash along convergent plate boundaries
Shield volcanoes - common along divergent plate boundaries and oceanic hot spots, usually quiet eruptions
Cinder cones - small steep-sided volcanoes that erupt gas-rich, moderately explosive