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Volcanoes and Volcanic Hazards

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  1. Volcanoes and Volcanic Hazards

  2. View From Space - Klyuchevskaya, Russia

  3. Cleveland Volcano, Alaska

  4. Mount Etna From Space

  5. Mount Etna From Space

  6. Mount Etna From Space

  7. Mount Etna

  8. Shiveluch, Russia

  9. Magma – molten rock beneath the surfaceLava – molten rock on the surface

  10. Where Does Magma Come From? • Earth’s interior is hot (25 C/km near surface = 1000 C at 40 km) • Pressure inhibits melting • Mantle is solid • Never far below melting point • Volcanoes fed by small pockets 0-100 km deep • Rising hot material may melt • Water can lower melting point

  11. Why Igneous Rock Classification Matters • Silica Content = Viscosity • Silica Content Governs Violence of Eruptions • Silica Poor (Basalt): Fluid lavas, generally little explosive activity • Intermediate Lavas (Andesite): Pasty lavas, explosive eruptions common • Silica-Rich Lavas (Rhyolite): Extremely viscous lava and explosive eruptions

  12. Basalt (45-52% SiO2) • Slightly modified planetary raw material • Derived directly from mantle • Oceanic crust • Hot Spots and Flood Basalts • Oceanic volcanic arcs • Early stage of continental volcanic arcs • Rift zones with rapid spreading • Fluid lava with little explosive activity • Shield volcanoes, Cinder Cones

  13. Plate Tectonics and Volcanoes

  14. A Cinder Cone:Wizard Island, Crater Lake, Oregon

  15. Paricutin, Mexico1943-1952

  16. Shield Volcano: Haleakala, Hawaii

  17. Andesite (52-66% SiO2) • Mixture of mantle material and continental crust • Continental volcanic chains • Pasty lava with significant explosive activity • Stratovolcanoes

  18. Plate Tectonics and Volcanoes

  19. Stratovolcano: Mount Shasta, California

  20. Stromboli

  21. Rhyolite (>66% SiO2) • Mostly remelted continental crust • Settings where magma has a long time to react with continental crust • Late stage of continental volcanic arcs • Slow-spreading Continental Rifts • Continental Hot Spots (Yellowstone) • Catasrtophic explosive activity common • Obsidian domes, magma chamber collapses

  22. Lava Dome, California

  23. Some Igneous Rocks Are Named on Textural Criteria • Pumice - Porous • Obsidian - Glass • Tuff - Cemented Ash • Breccia - Cemented Fragments

  24. Classes of Eruption Effusive • Icelandic • Hawaiian Explosive • Strombolian • Vulcanian • Plinian • Caldera-Forming (Ultra-Plinian) • Phreatic:

  25. Classes of Eruption

  26. Lava Flows Pyroclastic Debris Bombs Lapilli Ash Mudflows Landslides Gases Steam Carbon Dioxide H2S SO2 HCl HF Products of Eruptions

  27. Pollution SO2, HCl in Water Lava Flows Falling Ejecta Ash Falls Building Collapse Crop Destruction Mudflows Direct Damage (Colombia, 1985) Floods (Several Types) Blast (Mt. St. Helens, 1980) Pyroclastic Flow (St. Pierre, 1902) Gas (Lake Nyos, Cameroon, 1986) Environmental Hazards of Volcanoes

  28. Volcanic Hazards, Congo

  29. Nyiragongo, Congo • At least 34 eruptions since 1982 • Semi-permanent lava lake • Area accounts for 40% of Africa’s historic eruptions • Steep-sided but unusually fluid lava: unique • 1977: Lava lake drains at night, killing 70-hundreds • 2002: Lava invades city of Goma: 400,000 evacuated, 45 killed, 4500 buildings destroyed, 120,000 homeless

  30. Pyroclastic Flow or Nuee Ardente (French: Fiery Cloud)

  31. Welded Tuff, California

  32. How Calderas Form

  33. Crater Lake, Oregon

  34. Mount Mazama: After

  35. Mount Mazama: Before

  36. Jemez Caldera, New Mexico

  37. Valles Caldera, New Mexico

  38. Tuff, Valles Caldera, New Mexico

  39. Santorini (Thera), Greece

  40. Santorini (Thera), Greece

  41. Santorini, Greece

  42. Santorini, Greece

  43. Ash Layer, Santorini

  44. Ash Layers, Santorini

  45. What Really Destroyed the Minoan Civilization

  46. Volcanic Explosivity Index

  47. Collapsing Volcanoes – Mount Rainier

  48. Shastina and Landslide Deposit

  49. Mount Shasta and Landslide Deposit