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Volcanoes and Eruptions

Volcanoes and Eruptions. 8SCIENCE . Review. Where do volcanoes form? Plate boundaries How do volcanoes form? Heat and pressure from inside the Earth produces magma and pushes up to the surface What is a hotspot?

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Volcanoes and Eruptions

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  1. Volcanoes and Eruptions 8SCIENCE

  2. Review • Where do volcanoes form? • Plate boundaries • How do volcanoes form? • Heat and pressure from inside the Earth produces magma and pushes up to the surface • What is a hotspot? • Very hot areas in the mantle that produce volcanoes although they are not found on plate boundaries

  3. Types of Volcanoes • Shield • Cinder cone • Composite

  4. Shield volcanoes • Quiet eruption that produces lava and spreads out in flat layers • These layers build to form slightly sloping sides • Ex: Hawaiian islands produces 2 different types of lava: • Pahoehoe(smooth) - A’a (rough and chunky)

  5. Pahoehoe and A’a lava A’a lava Pahoehoe

  6. Cinder cone volcano • Explosive eruptions that throw lava and rocks high into the air • These bits of rock and hardened lava are called tephra • Tephra layers build up to form steep sided volcanoes

  7. Tephra lava Tephra lava erupted from the 1980 Mount St. Helens Eruption in Washington State

  8. Composite volcano • Produces eruptions that are quiet then violent • Cycles of lava and tephra form different layers • Usually found where one plate is forced under another

  9. What causes an eruption to be quiet or violent? • Amount of water vapor and other gases trapped in magma • High gas content = more violent eruption • Gases are trapped in magma and pressure builds up • As magma moves closer to the surface, there is less pressure and the gas can escape • Amount of silica (silicon and oxygen) present in magma • Low in silica = more quiet eruption

  10. Other volcanic structures • Not all magma flows to the surface • Some may rise from the volcano and cools underground to form other rock structures • Erosion of the rock layers make these visible to us today

  11. CALDERAS IN OREGON (US) AND PHILLIPINES DEATH VALLEY, CALIFORNIA SHIPROCK, NEW MEXICO COLOMBIA

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