volcanoes. what are volcanoes? a volcano is an opening in earth that erupts gases, ash, and lava
TRANSCRIPT
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VolcanoesVolcanoes
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What are volcanoes?What are volcanoes?
A volcano is an opening in Earth that erupts gases, ash, and lava.
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How do volcanoes form?How do volcanoes form?Magma is less dense than the rock
around it, so it is forced toward the surface
Vent: Opening that magma flows through
Crater: The steep-walled depression around a volcano’s vent
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Where do volcanoes occur?Where do volcanoes occur?Divergent Plate Boundaries
– Iceland– Mid-Atlantic Ridge
Convergent Plate Boundaries– Oceanic Plate slides beneath Continental
PlateAndes mountains in South AmericaErupt more violently
– Oceanic Plate slides beneath Oceanic Plate
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Where do volcanoes occur?Where do volcanoes occur?
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Where do volcanoes occur?Where do volcanoes occur?Hot Spots
– Areas between Earth’s mantle and core that are unusually hot.
– Hot rock forces toward the crust where it melts partially to form a hot spot.
– Hawaiian IslandsPacific Plate moving over a stationary hot
spot.
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Hot Spot Occurrence Hot Spot Occurrence
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What controls eruptions?What controls eruptions?
Trapped Gases
Composition of Magma–Silica Poor–Silica Rich–Varying Silica Content
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Liquid Hot Magma!!!!Liquid Hot Magma!!!!
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What controls eruptions?What controls eruptions?– Silica Poor: quiet eruption
Basaltic Magma, Pahoehoe flows
– Silica Rich: explosive eruption Granitic Magma, Mount St. Helens,
WA– Intermediate Silica: Quiet / explosive
eruption. Andesitic Magma, Convergent Plate
Boundaries, Krakatau, South America
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Forms of VolcanoesForms of VolcanoesShield Volcano
– Quiet eruptions of basaltic lava spread out in flat layers
– Layers buildup and form a broad volcano with gently sloping sides
– Hawaiian Islands
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Forms of VolcanoesForms of VolcanoesCinder Cone
Volcanoes– Explosive
eruptions throw lava and rock high into the air
– When rock and ash land, it forms a steep-sided, loosely packed volcano
– Paricutín, Mexico
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Forms of VolcanoesForms of VolcanoesComposite Volcano
– Varying explosions depend on amount of silica and trapped gases.
– Alternating layers of lava and ash form a volcano
– Mount Rainier, WA
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Violent EruptionsViolent Eruptions1883: Krakatau,
Indonesia
1906: Vesuvius, Italy
1983: Kilauea, Hawaii
2000: Popocatepetl, Mexico
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Volcanic Activity ReportsVolcanic Activity Reports
http://volcano.und.edu/vwdocs/current_volcs/current.html
http://www.volcano.si.edu/reports/usgs/