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
  • 5. 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
  • 6. 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
  • 7. 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
  • 8. 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
  • 9. CALDERAS IN OREGON (US) AND PHILLIPINES
    DEATH VALLEY, CALIFORNIA
    SHIPROCK, NEW MEXICO
    COLOMBIA