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Earthquakes

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Earthquakes Earthquakes Presentation Transcript

  •  
    • Volcano :
    • an opening in the earth’s surface through which lava, hot gases, and rock fragments erupt
    Introduction to volcanoes
      • Magma 50-100 miles below the earth’s surface slowly begins to rise to the surface
      • As the magma rises it melts gaps in the surrounding rock
      • As more magma rises a large reservoir forms as close as 2 miles below the surface (magma chamber)
    How do they form?
      • Pressure from the surrounding rock causes the magma to blast or melt a conduit (channel) to the surface where magma erupts onto the surface through a vent (opening)
    How do they form?
      • The magma, now called lava, builds up at the vent forming a volcano
    How do they form?
      • Often the volcano sides will be higher than the vent forming a depression called a crater
    How do they Form?
    • Crater :
    • Caldera:
    • an unusually large crater or the remains when the cone collapses into its own magma chamber
  • Anatomy of a Volcano
    • Cone :
    • the above ground structure built from lava and/or tephra
    • Conduit :
    • the path that magma takes from the magma chamber to the vent
    • Magma Chamber :
    • the reservoir located under the volcano where magma collects and becomes the supply of magma/lava to build the volcano
    • Lava:
    • molten, liquid rock on the surface of the earth
    • Parasitic Cone:
    • a smaller secondary volcano built on the side of or near the main volcano, but sharing the same conduit to the magma chamber
    • Fumarole:
    • a secondary vent that emits only gases
    • Fissure :
    • a long fissure ( crack ) from which lava flows
    • Vent : opening of the volcano, through which lava, ash and gases flow
  • What comes out of volcanoes?
    • Lava
    • Tephra
    • Gases
    • Lava— 3 kinds:
    • Pahoehoe lava:
    • Hot, thin, fast flowing
    • harden with a relatively smooth surface
    • Often has a ropy or wrinkled appearance
    • Pahoehoe lava:
    • Aa lava:
    • Cooler, thicker , slow moving
    • Hardens with a rough, jagged, sharp edge surface
      • Pillow Lava:
      • Lava suddenly cooled by water
      • shows sack-like segments (stuffed pillows)
  • Tephra
    • Basically, rock fragments
    • Also known as pyroclastic rock fragments.
    • There are many different possible sizes, from very small (volcanic ash or dust to much larger rocks (called volcanic bombs )
  • Ash & dust
  • Volcanic Bombs This dacite breadcrust bomb (about 15 cm in diameter) was erupted from the lava dome at Mount St. Helens, Washington.
    • Lahar (mudflow):
    • mixture of ash, eroded land , and water flowing down river valleys
    • Lahar (mudflow):
  • GASES
    • water vapor, carbon dioxide , nitrogen, sulfur dioxide , hydrogen sulfide, chlorine
  • Where do Volcanoes Occur?
  • Where do Volcanoes Occur? location Examples Divergent Boundaries : where plates move APART Iceland
  • Where do Volcanoes Occur? location Examples convergent Boundaries : where plates come together Cascade range volcanoes, Andes
    • Cascade Volcanoes
  • Where do Volcanoes Occur? location Examples Hot Spots : plates riding over an especially hot place in the mantle Hawaii, Yellowstone, Iceland
  • Hot Spots
      • Two factors determine the type of eruption :
      • Amount of water vapor & other gases in the magma
      • The chemical composition of the magma
    Types of Volcanic Eruptions
      • Trapped gases under high pressure will violently explode when the magma reaches the lower pressure of the surface.
    Explosive Eruptions
      • Has granitic magma is very thick and plugs the vent causing the pressure to build until it blows violently out the vent
    Explosive Eruptions Mt. St. Helens
      • The high water content of the magma produces more water vapor which when mixed in granitic magma produces explosive eruptions
    Explosive Eruptions Mont serrat
      • Low pressure gas
    Quiet Eruptions
      • Has basaltic magma (is more fluid and will flow instead of explode)
    Quiet Eruptions
      • … and has low water content
      • Examples : Hawaii
    Quiet Eruptions
  • Cinder cones
    • Small base, steep-sided, loosely consolidated
    • Up to 1000 feet tall
    • Life span of a few years
    • Commonly built from gravel size lava rock fragments called cinders
    • Violent eruptions, dangerous when close---High pressure gas bubbles causes thick lava to explode into the air, lava begins to cool as it rises and falls becoming very sticky
    • When lava hits the ground it sticks rather than flows
    • This builds a steep cone with a small base
  •  
      • Cinder Cones :
    Cinder Cones
  • Shield volcanoes
    • Large base, gentle slope , lava rock layers
    • A few miles high
    • Life span of a million years or more
    • The lava is hot, thin, very fluid often basaltic
    • Example: Hawaiian Islands, Iceland
  • Shield volcano on Mars; Taken from space Take a look at these examples: http://www.volcano.si.edu/world/tpgallery.cfm?category=Shield%20Volcanoes The Mauna Loa volcano in Hawaii—the largest volcano on Earth—has the broad expanse characteristic of shield volcanoes. It spreads across half the island of Hawaii.
    • Shield Volcanoes
    Mauna Kea Shield volcanoes
  • Composite or strato
      • Large mountain volcano often snow capped , a few miles high
      • Life span of million years or more
  • Composite or strato
      • Have alternating eruptions of tephra (air-borne) and lava . The tephra adds height to the volcano and the lava cements the tephra together and adds to the base .
      • Found mostly in subduction zones and have violent eruptions.
  • STrato/Composite Llaima Volcano, Chile.
      • Composite (strato) Volcanoes examples:
    Mt. Rainier Mt. Fuji Mt. Kilimanjaro
  • Composite/strato volcanoes
      • Active (awake):
      • Has erupted within recent time and can erupt again at any time .
      • Pre-eruption activities :
        • Increase in earthquake activity under the cone
        • increase in temperature of cone,
        • melting of ice/snow in the crater
        • swelling of the cone
        • steam eruptions
        • minor ash eruptions
    Volcano Activity Levels (Stages)
  • Mt St. Helens
    • Dormant (sleeping):
    • No eruption within recent times, but there is record of past eruptions
    • Can become active and erupt again after a “wake up” period
    • Example : Mt. Rainier
    • Extinct:
    • No eruption within recorded history
    • Not expected to ever erupt again
    • Example: Mount Mazama (Crater Lake)
  • Crater Lake
    • Mount Rainier
      • The most dangerous volcano in the US
      • The danger is mostly from lahars traveling down river valleys at a speed of 25mph and destroying everything in its path
      • 100,000 people live on the solidified mudflows of previous eruptions
    • Mount Rainier
      • The mountain is dangerously unstable , a tall, steep heap of loose rock held together by the force of gravity and a cubic mile of glacier ice that could be melted or shaken loose
      • Lahar flows average every 500 years and have gone as far as the Puget Sound lowlands
      • Mount Rainier has erupted 4 times in the last 4000 years with the last eruption 200 years ago
  •