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Volcanoes

Volcanoes. A Volcano is…. An opening in Earth’s crust through which molten rock, gases, and ash erupt. Also, the landform that develops around this opening. Why Volcanoes form.

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Volcanoes

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  1. Volcanoes

  2. A Volcano is… • An opening in Earth’s crust through which molten rock, gases, and ash erupt. • Also, the landform that develops around this opening.

  3. Why Volcanoes form • Volcanic Eruptions occur when magma rises to the surface. This will happen when the asthenosphere melts enough to flow. There are three things that can cause this: • 1- A decrease in pressure(like at a mid-ocean ridge or rift valley) • 2- An increase in temperature(like at a hot spot) • 3- An increase in the amount of water in the asthenosphere (like at subduction)

  4. Where Volcanoes Form • Most volcanoes occur at: • DIVERGENT boundaries, and at • CONVERGENT boundariesthat haveSUBDUCTION. • Hot Spots

  5. Volcanoes at Divergent Boundaries • Decrease in pressure as plates pull apartlets magma rise. • These fissure volcanoes are located at the Mid-Atlantic Ridge and the Great African Rift Valley

  6. Divergent- Great Rift Valley

  7. Volcanoes at Convergent Boundaries (Subduction) • Subductionincreases the amount of water in the asthenosphere,which lowers the melting temp. • As the denser oceanic crust is pushed lower, it melts into magma. • When continental and oceanic plates converge, a volcano forms on land. • When 2 oceanic plates converge together, a volcano forms an island. Mount Hood/ Portland

  8. Volcano- Convergent Sibayak, Indonesia Mt St.Helens

  9. Hot Spots • Sometimes, volcanoes occur at places that aren’t plate boundaries. • We call these HOT SPOTS. • Hot spots are areas where hot magma rises from deep in Earth’s mantle. • Magma escapes where the crust is the thinnest or weakest. • It starts out solid then it melts when it reaches areas of lower pressure.

  10. Example of Hot Spot • Volcanoes that make up Hawaii.

  11. Types of Volcanoes • There are 4 main types of Volcanoes: • Shield Volcanoes • Cinder Cone Volcanoes • Composite Volcanoes • Fissure Volcanoes

  12. Shield Volcanoes • Shield Volcanoes form from runny lava (low viscosity) that tends to flow long distances before hardening. They generally have quiet eruptions. • Volcano has a broad base and gently sloping sides. • Volcano has a less explosive eruption than other types because the lava flows more easily • Type of magma- Mafic Basalt: black, runny lava • Made oflayers of lava • Example: Mauna Loa, Hawaii

  13. Cinder Cones • Form when molten lava is thrown into the air from a vent. As it falls, it breaks into fragments called ash or tephra that harden before hitting the ground. • The ash and tephra make a cone-shaped mound. • They are smaller than other types. • Erupt explosively because magma is thick, which allows pressure to build up. • Magma composition: Felsic Rhyolite (light colored)

  14. Example: Krakatau, Indonesia

  15. Cinder Cones New Guinea Iceland

  16. Composite or Stratovolcano • Form from alternating eruptions of quiet lava and explosive ash. The layers build up and make a moderate-sized volcano. • Most common kind of volcano • Made oflayers of ash/tephra and lava. • Magma composition- Andesite: medium color

  17. Example of Composite/Stratovolocano • Mt. Pinatubo-Philippines

  18. Fissure Volcanoes • Form in long cracks where plates are pulled apart and near other volcanoes where the crust is weakened. Cinder Cone or Shield Volcanoes may also be nearby.

  19. Yellowstone • Check out how large some of the lava flows were from the Yellowstone Volcano!!!

  20. How does a Caldera Form? • A) A Volcano’s pressure starts to build up • B) The Volcano releases large amounts of Lava • C) As the Lava is released, the pressure decreases and the volcanic mountain begins to collapse, forming a concave shape in the center of the volcano. • D) The center of the volcanic mountain may begin to fill with water and form a lake.

  21. Crater Lake in Oregon State should actually be called Caldera Lake

  22. Label the parts of a volcano Word Bank: • Main Vent/Crater • Secondary Vent • Magma Chamber • Lava • Ash & Dust Cloud • Tephra Bombs • Cone

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