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VOLCANISM

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  1. VOLCANISM Mount St. Helens, 1980 eruption

  2. Where are volcanoes located?

  3. Volcanoes are located over divergent plate boundaries (mid-oceanic ridges)

  4. Laki fissure, Iceland

  5. Volcanoes are located over convergent plate boundaries (subduction zones)

  6. Mount Rainier, Tacoma, Washington

  7. Volcanoes are located over Hot spots

  8. What are the products of volcanism?

  9. Welded tuff (ash & flow deposits)

  10. Vesicular Basalt

  11. Pyroclastic eruption at Arenal Volcano, Costa Rica

  12. Volcanic Bombs

  13. Pyroclastic flow at Mount Unzen

  14. Volcanic Breccia

  15. WHY DO DIFFERENT VOLCANOES HAVE DIFFERENT SHAPES?

  16. Gentle-slopes (Shield Volcano)

  17. Gentle-slopes (Shield Volcano) Non-explosive eruptions Basaltic flows Low-viscosity Lava Low SiO2 content Mafic composition

  18. steep-slopes (Cinder-cone Volcano)

  19. steep-slopes (Cinder-cone Volcano) Pyroclastic material High SiO2 content More Felsic composition

  20. steep-slopes (Composite Volcano)

  21. steep-slopes (Composite Volcano) Alternating layers of Basaltic flowsand pyroclastic material Mafic-felsic composition

  22. Volcanic domes

  23. Volcanic domes Felsic lava Very high viscosity Lava accumulates over the vent

  24. Evolution of Crater Lake Caldera

  25. Mount St. Helens (Before eruption)

  26. Mount St. Helens (During eruption)

  27. Mount St. Helens (After eruption)

  28. Mount St. Helens (Before eruption)

  29. Hot Spots and Plate movement

  30. Volcanic Hazards

  31. Pyroclastic Flows are the most dangerous

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