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Volcanoes and Plate Tectonics (part 2)

Volcanoes and Plate Tectonics (part 2). “an opening in the Earth’s crust through which an eruption takes place”. Volcanoes Three types. Cinder Cones . Cinder Cone. Inside a Cinder Cone. Cinder Cone. Steep sloped sides (angles close to 40 °)

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Volcanoes and Plate Tectonics (part 2)

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  1. Volcanoesand Plate Tectonics (part 2) “an opening in the Earth’s crust through which an eruption takes place”

  2. VolcanoesThree types • Cinder Cones

  3. Cinder Cone

  4. Inside a Cinder Cone

  5. Cinder Cone • Steep sloped sides (angles close to 40°) • Relative to other volcanoes – small few hundreds of meters high • Small explosive eruptions • Made up of pyroclastic material (ash and tephra)

  6. Shield

  7. Montserrat Volcano eruption

  8. Shield Volcanoes • The volcano have a very broad base, with gently sloping side (like a ‘shield’) • Quiet eruptions • Made up of layers of hot, mafic (basaltic) lava • Hawaii is a good example of a shield volcano

  9. Composite

  10. Mount Saint HelensMay 15, 1980

  11. Mount Saint HelensMay 18 1980

  12. Mount Saint HelensMay 18, 1980 Eruption

  13. Mount Saint HelensMay 18 1980

  14. Mt. St. Helens devastation

  15. Mount Saint Helens September 10, 1980

  16. Mount Saint HelensSeptember 24, 1984

  17. Mount Saint Helens (from Spirit Lake) May 15, 1980

  18. Mount Saint Helens (from Spirit Lake) May 19,1982

  19. Popocatepetl composite volcano in Mexico is on the Ring of Fire

  20. Composite Volcanoes • Steep sloped sides • Very tall, 1000s of meters • Very explosive eruptions, sometimes quiet eruptions (alternating for the most part) • Made up of alternating layers of lava flows and silica rich (granitic) pyroclastic material. • Mt. St. Helens is a good example of a composite volcano

  21. Volcanoes (cont.) Kinds of Eruptions: Quiet Shield Volcanoes – broad base, low angle slope • Pillow lava – lava that occurs in mid-ocean ridges • Basalt Plateaus – lava spreading evenly over a large area

  22. Volcanoes (cont.) Kinds of Eruptions: • Rift Eruptions – Opening in the crust “spreading centers”: • sea floor spreading (ocean) • rift valley (continent) Lava ‘oozes’ out because of its mafic or basaltic composition

  23. Areas of Volcanic Activity(kinds of eruptions) Same regions as Earthquakes, which often serve as warning signs that a volcanic eruption might occur. • Ring of Fire – around the rim of Pacific Ocean, subduction zone • Ocean Ridge system • Hotspots

  24. Volcanoes (cont.) Kinds of Eruptions: Ring of Fire – Subduction boundary Eruptions – Cinder cones and Composite Volcanoes Explosive eruptions, usually young mountain chains – like around the Ring of Fire

  25. Hot Spots Hot Spots – a place in the mantle where great amounts of heat are rising through the lithosphere. • Causes of Hot Spots are still unknown – the source of the heat or ‘spot’ remains in the same location while the plate moves over it. • For example: Hawaii

  26. Hot Spots

  27. Hot Spots

  28. Thermal signature of the Hawaiian Islands

  29. Plutonic – Igneous Rocks When masses of magma cools beneath the surface, it forms the cores of mountains. • These ‘igneous intrusions’ are called Plutons. Plutons have different names depending on their size and shape

  30. Plutonic – Igneous Rocks Small intrusive igneous formations are: • Dikes • Sills • Volcanic Necks • Laccoliths…

  31. Plutonic – Igneous Rocks • Laccolith – magma that buldges upward and formed dome mountains. (Henry Mountains, Utah and Black Hills, South Dakota) • Batholith – a LARGE body (> 100 km3) of intrusive igneous rock. Forms the core of most mojor mountain ranges (Sierra Nevada) • Stock – small batholith, less than100 km3

  32. Volcanoes

  33. Ruby Mountains Batholith

  34. La Paz Batholith

  35. East side of Sierra Batholith

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