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Volcanoes

Volcanoes. Different Volcanic Settings. Types of Eruptions. Eruptions will generally be of two types: Quiet (Rift) eruptions Explosive (Subduction) eruptions Each will produce a different type of volcanic cone (shield or composite) . RIFT (Quiet) ERUPTIONS.

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Volcanoes

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  1. Volcanoes

  2. Different Volcanic Settings

  3. Types of Eruptions Eruptions will generally be of two types: • Quiet (Rift) eruptions • Explosive (Subduction) eruptions • Each will produce a different type of volcanic cone (shield or composite)

  4. RIFT (Quiet) ERUPTIONS • Generally at hot spots, spreading plates • Mantle comes directly to surface • Hot lava; low viscosity, flows easily, gases escape easily, mafic lava • Forms shield volcanoes, flood basalts

  5. SUBDUCTION (Explosive) ERUPTIONS • Found at subduction zones • Magma low temperature, high viscosity, does not flow easily, gases trapped, hard to predict explosions of felsic lava • Forms composite (strata) volcanoes, cinder cones, calderas, ash, lapilli, bombs, gas flows, very destructive

  6. Shield Volcanoes • broad, gently sloping cones • constructed of solidified lava flows • lava spreads widely and thinly due to its low viscosity • produces a volcano in the shape of a flattened dome or ‘shield’

  7. Composite (Strata) Volcanoes • constructed of alternating layers of pyroclastics (ash and rock particles) and rock solidified from lava flows. • built over long spans of time • eruption is intermittent, (a few years of intense activity separated by hundreds or thousands of years of inactivity) • most of the better known volcanoes of the world are composite volcanoes.

  8. Composite Volcanoes

  9. Shield and Composite Volcanoes Figure 12.32

  10. Composite Volcano Columbia River basalt flow (Ancient Shield)

  11. Some Interesting Volcano Facts

  12. Pyroclastic flows are superheated gas and particles (ash & dust or larger cinders, blocks or bombs) • At Mt. St. Helens’s the pyroclastic flow extended up to 8 km with a temp of 700 C • Mount Pelee, (Carribean island of Martinique) - 1902 eruption killed all but 2 of the more than 20,000 people in the town of St. Pierre

  13. Ashfall • Ash from eruptions that falls on surrounding ground • When ash is carried to high altitudes this can spread great distances

  14. MOUNT ST. HELEN’S Before 1980 Eruption May 18, 1980 After 1980 Eruption

  15. Mt. Pinatubo Philippines June 1991

  16. Volcanoes & Environment • brilliant sunsets and sunrises due to fine ash and gases in the stratosphere, (cloud drifts around world) • Mt. Pinatubo - 22 million tons of sulfur dioxide (SO2) formed droplets of sulfuric acid • blocked some sunlight from reaching Earth, cooling temperatures worldwide by 0.5 C • An eruption the size of Mount Pinatubo could affect the weather for a few years.

  17. ANAK KRAKATAU: (Child of Krakatoa) • August 26,1883, Eruption destroyed much of the island of Krakatau ("Krakatoa") in Indonesia, • One of the most catastrophic natural disasters in recorded history (heard more than 3000 miles away) • Fine ashes from the eruption were carried by upper level winds as far away as New York City. • Volcanic dust in the upper atmosphere affected incoming solar radiation and the earth's weather for several years.

  18. series of large tsunami waves followed main explosion, some nearly 40 meters above sea level • more than 36,000 people in the coastal towns and villages killed • Tsunami waves were recorded or observed throughout the Indian Ocean, the Pacific Ocean, the American West Coast, South America, and even as far away as the English Channel.

  19. April 1815 - Tambora Volcano, Indonesia the most powerful eruption in recorded history. • Tambora's volcanic cloud lowered global temperatures by as much as 3 C • Even a year after the eruption, most of the northern hemisphere experienced sharply cooler temperatures during the summer months. • In parts of Europe and in North America, 1816 was known as "the year without a summer."

  20. Mt. St. Helen’s - Oct. 1, 2004 Mt. St. Helen’s - Oct. 5, 2004

  21. Mt. St. Helen’s Oct. 12, 2004 Mt. St. Helen’s Today

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