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  • 1. Volcanoes
  • 2. How Volcanoes Form
    • volcano: a mountain that forms when red hot melted rock flows through a crack into the earth’s surface
      • magma: melted rock inside the Earth
      • lava: melted rock that reaches the Earth’s surface
  • 3.
    • volcanoes form ocean floors
      • plates move apart and magma slowly rises toward the surface from deep in the mantle
      • magma gets to the surface - cools, hardens and forms new ocean floor
    • volcanoes form when plates move toward each other
      • plates collide one plate is forced down into the mantle - melts partly
      • magma rises through the vent to form mountains
        • vent: a rocky tube that carries magma to the surface
      • Andes in South America and Cascade Range in the NW US formed this way
  • 4. The Andes in South America Cascade Range in NW US
  • 5.
    • volcanoes form when a plate moves over a hot spot in the mantle
      • fountains of hot rock punch through the crust to form volcanoes
    • volcanic islands of Hawai’i formed this way
    Hawaiian Volcanoes
  • 6. Types of Volcanoes
    • Shield volcano : large mountains with gentle slopes
      • form from runny lava
      • many volcanoes in Hawai’i are shield volcanoes
        • the largest is Mauna Loa on the main island and is about 30,000ft from the ocean floor
  • 7.
    • Cinder cone volcanoes : small volcanoes made of hardened lava chunks called cinders
      • steep sides
      • usually less than 1000 ft tall
  • 8.
    • Composite volcanoes : medium sized moutains
      • made of layers of alternating layers of lava and cinders
      • have steep peaks and gently sloping sides
      • Mount Fuji in Japan, Mount Pelee on the island of Martinque, and Mount Vesuvius in Italy were formed this way
  • 9. Mount Fuji in Japan Mount Pele on Martinque Mount Vesuvius
  • 10. Volcanoes Build
    • volcanic eruptions form new crust on continents
      • volcanoes add to Earth’s landscape
        • Crater Lake in Oregon
    • volcanic eruptions have good effects on the land around them
      • soil around an active volcano has minerals that help crops grow - minerals are added when water flows over the rock
        • many types of plants grow in the soil surrounding the slopes of Mout Vesuvius
        • fruits and vegetables grow well near the bottom
        • Hardwood trees grow well in the soils on the slopes
  • 11. Volcanoes Destroy
    • lava and gases that erupt from volcanoes are very hot and often destroy everything in their path
      • Mt. St. Helens in WA erupted in 1980 - temp of ashes and gases reached 1470 degrees F
      • blast blew down trees 15 mi away
      • 60 people died
    • clouds of ash and gases were so thick people couldn’t breath
  • 12.  
  • 13.
    • 1983 Colo volcano on the Indonesian island of Una Una erupted
      • scientists were able to warn people
      • 7000 peole who lived in the area went to safe places
      • when the volcano erupted much was destroyed but nobody died
  • 14. Summary
    • Volcano is a mountain that forms when melted rock called lava flows out onto the Earth’s surface
    • Most volcanoes form along plate edges
    • Volcanic eruptions add crust to the Earth and can be harmful
    • Lava flows can make soils rich in minerals that help crops grow