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Volcanic Activity

Volcanic Activity. Plumbing System of a Volcano. Fig. 5.1. Cross Section of the East Pacific Rise. Fig. 5.29. Volcanic Materials. Lavas – appearance depends upon viscosity Low viscosity – low SiO 2 lavas; high T; low volatile content - smooth lava

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Volcanic Activity

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  1. Volcanic Activity

  2. Plumbing System of a Volcano Fig. 5.1

  3. Cross Section of the East Pacific Rise Fig. 5.29

  4. Volcanic Materials • Lavas – appearance depends upon viscosity • Low viscosity – low SiO2 lavas; high T; low volatile content - smooth lava • High viscosity – high SiO2 lavas; low T; high volatile content – rough lava • Pyroclastic material – fragmented material due to explosive volcanic activity • Associated with magmas with high volatile gas content • Volcanic gases – water, carbon dioxide, sulfur, sulfur dioxide, hydrogen sulfide

  5. Basaltic Lavas • Pahoehoe – rope-like, glassy • Aa – fragmented, dull surfaces Aa Pahoehoe

  6. Basaltic Lavas • Pillow lavas – underwater “pillow” or “tube” shaped lava flow

  7. Pyroclastic Materials • Pyroclastic name based upon fragment size ash – sand size lapilli – walnut size bombs (> 1 inch, cools in flight) blocks (> 1 inch, solid before ejection)

  8. Volcanic Bombs

  9. Volcanic Blocks

  10. Volcanic Tuff

  11. Volatile Gases Associated with Volcanism • Steam (H2O) • Carbon dioxide (CO2 ) • Hydrogen sulfide (H2S) • Sulfur vapor • Many other constituents

  12. Sulfur-encrusted fumerole: Galapagos Islands Sulfur-encrusted fumerole:Galapagos Islands Fig. 5.26 Christian Grzimek/Photo Researchers

  13. Volcanic Landforms • Shield volcanoes • Cinder cones • Sratovolcanoes or composite volcanoes • Domes • Calderas • Volcanic Necks and Pipes • Fissure Eruptions

  14. Shield Volcanoes • Very large • Composed of low viscosity basalt • Volcanoes have a gentle, shield shape • Example: Mauna Loa, Hawaii

  15. Mauna Loa, Hawaii

  16. Shield Volcano Fig. 5.10

  17. Cinder Cone • A relatively small volcanic cone composed of unconsolidated pyroclastic material • Cinder cones may be composed of basalt, andesite, or rhyolite fragments • Usually active for a short period of time • Example: Paŕicutin, Mexico

  18. Cinder Cone Fig. 5.12

  19. Paŕicutin, Mexico

  20. Paŕicutin, Mexico

  21. Cerro Negro Cinder Cone, near Managua, Nicaragua in 1968 Fig. 5.13 Mark Hurd Aerial Surveys

  22. Stratovolcanoes or Composite Volcano • Steep, symmetrical volcanic cones • Composed of alternating layers of lava and volcanic ash • Usually composed of andesitic material • Examples: Fujiyama, Japan; Mt. Saint Helens, Wa

  23. Stratavolcano

  24. Fujiyama, Japan

  25. Mount Saint Helens – Before May 1980 Mount Saint Helens, Before May, 1980 Emil Muench/Photo Researchers

  26. After May, 1980 Mount Saint Helens – After May, 1980 David Weintraub/Photo Researchers

  27. Volcanic Domes • Small, dome or “inverted” cup-shaped landforms • Usually composed o rhyolie • Example: Lava Dome in the Mount Saint Helens crater

  28. Fig. 5.11

  29. Mount St. Helens lava dome Lava Dome Fig. 5.11 Lyn Topinka/USGS

  30. Inyo Obsidian Domes-California P. L. Kresan

  31. Caldera • A large, circular depression produced by the collapse of a volcano following the emptying of a subterranean magma chamber • Example: Crater lake, Oregon

  32. Formation of a Caldera Fig. 5.16

  33. Crater Lake, Oregon Fig. 5.17 Greg Vaughn/Tom Stack

  34. Volcanic Necks and Pipes • Remnants of volcanic vents and conduit systems • Exposed after erosion has removed the surrounding, soft volcanic rubble and country rock • Examples: Shiprock, N.M.

  35. Shiprock, N.M.

  36. Fissure Eruptions • Very extensive, sheet-like lava flows that originate from long cracks (fissures) rather than central vents or volcanoes. • Flood lavas or basalts are associated with this type of activity • Example: Columbia river basalts, Washington and Oregon

  37. 1971 Fissure Eruption, Kilauea, Hawaii

  38. Fissure Eruptions Form Lava Plateaus Fig. 5.20

  39. Extent of Columbia River Basalts Fig. 5.22

  40. Columbia Plateau Flow Basalts Fig. 5.2 Martin G. Miller

  41. Relationship of Volcanism and Plate Tectonics • Volcanoes of the Earth are associated with: • Plate Boundary Volcanism Divergent Plates Convergent Plate • Interplate Volcanism Hot spot or plume volcanoes

  42. The World’s Active Volcanoes Fig. 5.28

  43. Volcanism Associated with Plate Tectonics Fig. 5.30

  44. Types of Volcanic Hazards • Lava Flows: e.g. Hawaii, 1998 • Gas: e.g. Lake Nyos (Cameroon), 1984 • 1700 people killed • Ash fall: e.g. Mt. Pinatubo, 1991 • Pyroclastic flows: e.g. Mt. Pelee, 1902 • 28,000 killed • Lahars (mudflows): e.g. Nevado del Ruiz, 1985 • 23,000 killed • Tsunami: e.g. Krakatoa, 1883 • 36,417 killed

  45. Volcanic Hazards • Basaltic lavas (flows) may cover homes and roads, but flows move so slow that there is little loss of life

  46. May 1990 Eruption of Kilauea, Hawaii James Cachero/Sygma

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