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Description of volcanoes

Description of volcanoes

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  • 1. Volcano Notes
  • 2. Individual Volcanoes - Locations
    • Subduction Zones:
      • Association between volcanoes & subduction zones.
      • Ring of Fire = Ring of Subduction Zones
    • Continental Rift Zone:
      • A few volcanoes are associated with rift zones.
      • e.g. Kilimanjaro & others in east African rift.
    • Hot Spots:
      • Some coincide with plate boundaries, most don’t.
      • e.g. Hawaii
      • Galapagos Is., Iceland, Yellowstone.
  • 3. Where are volcanoes located? Is there a pattern? AT PLATE BOUNDARIES
  • 4.
    • Patterns:
    • Not random
    • Linear
    • Around large inactive plates
    • Near areas where elevation is changing
  • 5. Ring of Fire There are currently about 1500 active volcanoes around the world
  • 6. Volcanoes
    • Not currently erupting (but still could anytime)
      • Dormant (still has seismic activity and lava flow)
    • Currently erupting
      • Active
    • Not able to erupt (permanently)
      • Extinct (no seismic activity, no magma flow)
    • Magma
      • Molten rock material under the surface of the earth
    • Lava
      • Molten rock material above the surface of the earth
  • 7. Volcanoes
    • The largest most recent eruption in the US was Mt. St. Helens in Washington State in 1980
    • The largest most recent eruption outside of the US was Mt. Pinatubo in the Philippine Is. In 1991
    • Mt. Kilauea in Hawaii is the world’s most active volcano
  • 8. Volcanoes
    • The largest volcanic eruption of the twentieth century occurred on the Alaskan Peninsula ( Novarupta – 1912)
  • 9. Volcanoes
    • How do volcanoes form?
      • Deep inside the earth, heat and pressure cause rock to melt and form magma
    • Why is magma forced upward toward the earth’s surface?
      • Magma is less dense than the rock around it, so it is forced upward towards the earth’s surface
  • 10. Volcanoes
    • The opening at the top of a volcano is a
      • Vent
    • The steep walled depression around the vent is the
      • Crater
  • 11. Volcano Structure
  • 12. Volcanoes
    • Where do volcanoes occur?
      • Along plate boundaries and above hot spots AND rift boundaries
    • A hot part in the middle of the mantle that melts rock that is then forced upward as magma
      • Hotspot
  • 13. Volcanoes
    • An example of a volcanic area at divergent plate boundaries
      • Mid Atlantic Ridge
    • An example of a volcano at convergent plate boundaries
      • Soufriere Hills Volcano
        • (Montserrat, West Indies – 1995)
  • 14. Volcanoes
    • Volcanic eruptions can be
      • Explosive
      • Violent
      • Quiet
    • What 3 factors control the style of a volcanic eruption
      • Water Vapor
      • Amount of trapped gases
      • Magma composition
  • 15. Volcanoes
    • A volcanoes form depends on whether it is the result of a QUIET or and EXPLOSIVE eruption and whether it is made a silica-rich or silica-poor lava.
  • 16. Magma! What is the difference between “lava” and “magma”? Magma is below ground and lava is above ground.
  • 17. Measuring Volcanoes
  • 18. Novarupta
  • 19. Volcanoes
    • Shield Volcano: A broad volcano with gently sloping sides, quiet eruptions, silica-poor lava. (ex. Hawaiian Islands)
  • 20.  
  • 21. Volcanoes
    • Cinder Cone Volcano: steep sided volcano, explosive eruptions that throw lava and rock in the air, silica-rich lava (ex. Paricutin in Mexico)
  • 22.  
  • 23. Volcanoes
    • Composite Volcano: a small volcano, both quiet and violent eruptions
    • (ex. Mt. St. Helens)
    • Also called “stratocones”
  • 24.  
  • 25. Volcanic (lava) Domes
    • A volcanic dome is created when a body of viscous lava slowly pushes its way upward.
    • An example is the Dome formed in crater left by 1980 eruption (explosion) of Mount St. Helens.
  • 26. Volcanic (Lava) Dome Shape
  • 27. Lava Dome
  • 28. Volcanoes
    • Tephra: pieces of rock and solidified lava that fall from the air.
  • 29. Igneous Rocks
    • Volcanic eruptions are the results of the activity of igneous rocks.
      • Intrusive Rock formed when magma cools UNDER the ground
      • Extrusive Rock form when magma cools ABOVE the ground
  • 30. Igneous Rock Features
    • Batholiths – largest igneous rocks formed when magma cools underground .
    • Dike – magma that is squeezed into a generally VERTICAL crack that cuts across rock layers and hardens
    • Sill – magma that is squeezed into a HORIZONTAL crack between rock layers and hardens
  • 31. Volcanoes
    • Volcanic Neck- the solid igneous core of a volcano left behind when a volcano stops erupting
    • Caldera – large opening formed when a volcano collapses
  • 32. Caldera formation
  • 33.  
  • 34. Volcanoes
    • Igneous Rock – formed when magma hardens below the ground. Eventually, the process of erosion wears down rock at the surface, exposing features such as
      • Batholiths
      • Dikes
      • Sills
  • 35. Hot Spots
    • Areas of volcanic activity in middle of a plate
    • Exact cause is unclear, possibly due to hot area of magma under the lithosphere
    • There are two equally valid hypotheses that might explain hot spots:
      • The plate could be moving over a stationary hot plume in the mantle, or the hot area causing the volcanic activity may be moving under a static, unmoving surface. At this point in our explorations, we are unable to confirm one or the other hypothesis--each is worthy of consideration.
  • 36. Examples of Hot Spots
  • 37. Hot Spot Forming Islands
  • 38. Hawa’ii
  • 39. Cascade Range Volcanoes
  • 40. Cascade Eruptions – 2000 B.C. to Present
  • 41. Volcanic Results
  • 42.  
  • 43.  
  • 44. Volcanic Mud Flow (Lahar)
  • 45. Pyroclastic Flows This eruption of Mt. Pinatubo caused LOWER GLOBAL TEMPERATURES
  • 46.  
  • 47.