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19.4: Volcanoes

19.4: Volcanoes. Objectives . Describe different types of volcanoes Explain how and where volcanoes occur. Active and Extinct Volcanoes. Magma vs. Lava. Underground liquid rock. Once magma has broken the earth’s surface, it becomes lava. Types of Volcanoes .

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19.4: Volcanoes

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  1. 19.4: Volcanoes

  2. Objectives • Describe different types of volcanoes • Explain how and where volcanoes occur

  3. Active and Extinct Volcanoes

  4. Magma vs. Lava • Underground liquid rock • Once magma has broken the earth’s surface, it becomes lava

  5. Types of Volcanoes • Shield Volcanoes • Composite Volcanoes • Cinder Cones

  6. Shield Volcanoes • Magma rich in iron and magnesium is very fluid and flows easily • Eruptions are mild • Builds a gently sloping mountain • Hawaii

  7. Shield Volcanoes

  8. Composite Volcanoes • Alternating layers of ash, cinders, and lava • Magma rich in silica is thicker and traps gases • Gases in magma cause more explosive eruptions • Mt Fuji, Mt St Helens, Mt Hood, Mt Shasta, Mt Rainier

  9. Composite Volcanoes

  10. Cinder Cones • Smallest and most abundant type • Violent eruptions from lots of trapped gas • Short lifespan • Mt Paricutin in Mexico • First erupted in 1943 • In 2 years was 450 meters tall • Stopped erupting in 1952

  11. Cinder Cones

  12. Supervolcanoes

  13. If you haven’t been to Yellowstone – you need to go

  14. My favorite – the mudpots

  15. Yellowstone’s Debris Zones

  16. Colossal sized eruptions • Earth Changing • Currently 7 known, 3 in US • We are finding more

  17. Now total 8 • The Discovery Channel has documented seven known supervolcanoes • Yellowstone (Wyoming), • Long Valley (Mammoth, California), • and Valles Calderas (New Mexico) in the US; • Lake Toba, North Sumatra, Indonesia; • TaupoVolcano, North Island, New Zealand; • AiraCaldera, Kagoshima Prefecture, Kyūshū, Japan; • and the Siberian Traps, Russia • The newest: Sesia Valley Caldera in Northern Italy

  18. Valle Caldera, New Mexico

  19. Volcanoes form along plate boundaries and above hot spots • Openings in the earth’s crust are called vents

  20. Volcanoes at Convergent Plate Boundaries • 75% of all active volcanoes on Earth are located on Convergent Plate Boundaries • The Pacific “Ring of Fire” • The sinking ocean plate melts and magma rises to the surface • The lava is cooler, sticky and gaseous • Forms Composite volcanoes

  21. Volcanoes on Divergent Plate Boundaries • Magma rises to fill the gap, forming ridges around a central valley • San Luis Valley is formed this way • Mid-Atlantic Ridge and Iceland

  22. Volcanoes on Hot Spots • Some volcanoes form in the middle of plates • The form above mantle plumes • Hawaiian Islands • Yellowstone

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