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Volcanoes

Volcanoes. CHAPTER 5. What is a Volcano?. A mountain that forms when molten rock, called magma, is forced to the Earth’s surface Volcano belts form along plate boundaries. Where are volcanoes located?. Along tectonic plate boundaries The Ring of Fire. Sea Floor Spreading (Divergence).

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Volcanoes

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  1. Volcanoes CHAPTER 5

  2. What is a Volcano? • A mountain that forms when molten rock, called magma, is forced to the Earth’s surface • Volcano belts form along plate boundaries

  3. Where are volcanoes located? • Along tectonic plate boundaries • The Ring of Fire

  4. Sea Floor Spreading (Divergence)

  5. How a volcano is made… • Oceanic-Continental Convergence • Subduction Zones • (Most volcanoes)

  6. Oceanic-Oceanic Convergence

  7. Lava at the bottom of the ocean

  8. Hot Spots • So what about Hawaii? Or Yellowstone? • Volcanic eruptions can occur in the middle of a tectonic plate.

  9. Hot spots are places on Earth that are directly above columns of rising magma. These columns are deep within the Earth’s mantle Scientists still aren’t sure why they form…

  10. Hawaii • An example of a hot spot • Hawaii is a chain of islands that are located above a hot spot • Since, Hawaii is on a plate that moves and the hot spot’s location is permanent… • The Hawaiian islands are growing!

  11. Video clip about hot spots Video clip about Hawaiian eruptions

  12. Lava or Magma? • What’s the difference? • Lava • magma that flows onto the Earth’s surface • Magma • molten rock that forms inside the Earth

  13. Cross Section of a Volcano

  14. Types of Volcanic Eruptions • Quiet • Explosive

  15. Quiet Eruptions • Lava flows • Rivers of red-hot lava • Pours out calmly • Lava flows repeatedly and can cool to form large mountains

  16. Lava • Consistency can be thick (aa) or thin (pahoehoe) • Thinner lava will flow faster

  17. Explosive Volcanoes • Clouds of hot debris and gases shoot out from volcano • Magma explodes out • molten rock is blown into millions of pieces that harden in the air • The debris can also come from the solid rock from the mountain

  18. Pyroclastic Flow • Debris that is blown from the volcano • Rock fragments come in all sizes • Dust-sized • Boulder-sized • Come from explosive eruptions

  19. Pyroclastic Flow Continued… Flows are very hot ~200-700 Celsius (400 F – 1300 F) They also move very fast More than 80 km/hour (50 mph)

  20. Magma • Different types of magma are associated with different types of eruptions • What composition creates an explosive eruption? • High water content • High silica content

  21. Magma • High Water Content • Explosive eruptions • Pressure builds up when there is a lot of water. This pressure creates a very large, explosive eruptions.

  22. Magma • High Silica Content • Remember back to minerals….. • Also, explosive eruptions • Thick, stiff consistency • Flows slowly • Can harden in the volcano and plug the vent, causing pressure to increase • Creates a very explosive and large eruption

  23. Silica Content • High silica content • Thick magma makes it harder for gases to release/escape. • Low silica content • Magma is thin and runny. Gases can easily escape from it, so the eruptions are nonexplosive.

  24. Types of Volcanoes • Cinder Cone Volcanoes • Composite Volcanoes • Shield Volcanoes

  25. Cinder Cone Volcanoes • Smaller in size • High Silica Content (thick & sticky) • Made entirely from pyroclasticmaterial • Moderately explosive • Steep slopes • Cone shaped

  26. Examples • Flagstaff, Arizona • Paricutin, Mexico

  27. Composite Volcanoes • AKA: stratovolcano • Silica content varies (high and low) • Highly explosive eruptions • Pyroclastic flows, followed by outpourings of lava • Layers of lava followed by layers of ash • Broad bases and sides get steeper toward the top

  28. Examples • Mount Fuji, Japan • Last erupted in 1708 • Scientists believe its overdue for another eruption

  29. More Examples • Mount St. Helens • Last eruption, 1980

  30. Mount St. Helens

  31. Mount Vesuvius, Italy -Herculaneum and Pompeii Tragedy (79 AD) • Watch video clip about eruption

  32. Shield Volcanoes • Nonexplosive eruptions • Lava is very runny (low silica content) • Layers of lava build a dome-shaped volcano • Gentle sloping slides

  33. Examples • Hawaii volcanoes • Mauna Kea (largest mountain on Earth) • Kilauea

  34. Sources • www.volcanoes.com • http://www.decadevolcano.net/photos/merapi_may_2006_2.htm • http://www.terragalleria.com/parks/np-image.havo3690.html • http://volcanoes.usgs.gov • www.geology.sdsu.edu

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