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Continuation of earth’s process part 2
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Volcanoes Mountains that form when layers of lava and volcanic ash erupt an build up Most of the Earth’s volcanoes are dormant
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Volcanoes Deep in the Earth, rocks melt to form magma, and is called lava when it flows out into the surface through opennings called vents (the openning at the top is called the crater) These magma cools forming layers of rocks (igneous)
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Volcanic Ejecta Pahoehoe Pillow Lava Lava Tunnel Aa
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Pyroclast Volcanic materials ejected primarily made up of rocks, dust and gases
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Where Do Volcanoes Occur?
Divergent Boundaries Rifts are long, deep cracks in between plates that separate Magma flows on rifts as lava and is instantly cooled by sea water Lava builds up from the sea floor and volcanoes rise above sea level, forming islands
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Where Do Volcanoes Occur?
Convergent Boundaries Magma that is created from the subduction zone works it way to the surface forming volcanoes
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Where Do Volcanoes Occur?
Hot Spots Areas not on plate boundaries Some areas in the mantle are hotter than other areas Hotspots melt rocks which then rises toward the crust as magma
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Factors that Affect Eruptions
Amount of water vapor ang other gases trapped in the magma Rock composition of magma (basaltic or granitic) Basaltic magma – contains little silica, very fluid, and produces quiet, non explosive eruptions Granitic magma – contains lots of silica, has high water content, very thick, and produces violent and explosive eruptions
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Major Types of Volcanoes
1. Shield Volcano With broad, shield-like profiles, are formed by the eruption of low-viscosity lava (basaltic) that can flow a great distance from a vent, but not generally explode catastrophically. More common in oceanic than continental settings.
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Mauna Loa, Hawaii
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2. Cinder Cone or Scoria Cone Volcano
Once lava is thrown into the air, it cools and hardens (tephra) When it falls, it forms a steep-sided, loosly consolidated cinder cone volcano
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Paricutin Volcano, Mexico
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3. Composite Volcano Formed from an alternating layer of tephra and lava
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Mt. Fuji, Japan
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Mayon Volcano, Philippines
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Other Types of Volcanoes
Flat, linear cracks through which lava emerges
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Lakagigar fissure vent, Iceland
Krafla Volcano, Iceland
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After the explosion of a volcano, its top colapses down into the vent forming a very large opening called a caldera
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Taal Volcano, Philippines
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