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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. Identify the cause of each volcano below using the words: subduction, rift, and hot spot. • a) In 1973, a town in Iceland called Vestmannaeujar was surprised when lava began erupting from a vent or crack in the Earth’s surface. The Earth’s crust seemed to split apart._______________________ • b) Scientists feel that the Cascade Mountains, extending from California to British Columbia, are still forming. Two plates are colliding, forcing magma up from the mantle to form the mountain. _____________________ • c) Mauna Loa in Hawaii is the “growing mountain”. In 1969 and 1974, it erupted and poured out lava through a hole in the Earth. This lava called and hardened into rock. Below it, molten lava continues to flow. _____________________

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

  5. Introduction to the three types of volcanoes • Threetypes of volcanoes • As you view the video clip, try to think of some of the similarities and differences between the three types of volcanoes.

  6. 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)

  7. Pahoehoe and A’a lava A’a lava Pahoehoe

  8. 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

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

  10. 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(subduction zone)

  11. Let’s review with animations… • Types of Volcanoes

  12. 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

  13. 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

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

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