volcanoes. what are volcanoes? a volcano is an opening in earth that erupts gases, ash, and lava
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VolcanoesVolcanoes
What are volcanoes?What are volcanoes?
A volcano is an opening in Earth that erupts gases, ash, and lava.
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
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
Where do volcanoes occur?Where do volcanoes occur?
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.
Hot Spot Occurrence Hot Spot Occurrence
What controls eruptions?What controls eruptions?
Trapped Gases
Composition of Magma–Silica Poor–Silica Rich–Varying Silica Content
Liquid Hot Magma!!!!Liquid Hot Magma!!!!
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
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
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
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
Violent EruptionsViolent Eruptions1883: Krakatau,
Indonesia
1906: Vesuvius, Italy
1983: Kilauea, Hawaii
2000: Popocatepetl, Mexico
Volcanic Activity ReportsVolcanic Activity Reports
http://volcano.und.edu/vwdocs/current_volcs/current.html
http://www.volcano.si.edu/reports/usgs/
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