Dormant for 200 years


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Dormant for 200 years

  • Dormant for 200 years

  • Woke up in 1990; erupted into 1992

  • Lots of pyroclastics

  • Killed the Krafts and Harry Glicken, a survivor of Mt. St. Helens

  • Site of volcano warning system


50 60 erupt each year

  • 50 60 erupt each year

    • 3 4 in the US (mostly in Alaska)
    • Many potentially active in northwestern US and Alaska
  • Often at remote locations

  • Sometimes near population centers

    • Japan
    • Philippines,
    • Mexico
    • Indonesia






Mostly along plate boundaries; 80% in the "ring of fire“.

  • Mostly along plate boundaries; 80% in the "ring of fire“.

  • Molten rock, including small components of dissolved gases, produced where lithospheric plates interact with other earth materials is called MAGMA

  • Lava- magma from a volcano





Shield volcanoes

  • Shield volcanoes

    • Largest type
      • Hawaii
      • Iceland
      • Indian Ocean Islands
    • Gentle slopes (about 10° )
    • Among the tallest mountains
    • Generally non explosive eruptions: low silica basaltic flows
    • Some occurrences
      • Pyroclastic materials (tephra)
      • Lava tubes
      • Calderas
      • Rift zones (normal faults)


Cinder cones

  • Cinder cones

    • Much smaller (few km2)
    • Steeper (>30 35°)
    • Mostly pyroclastic materials
    • Easily eroded-poorly preserved
    • Often initial phase


Composite/Stratovolcanoes

  • Composite/Stratovolcanoes

    • Many in NWUS (Rainier, St. Helens, Hood)
    • Andesitic (intermediate)
    • Layers of andesite/ pyroclastics
    • Slopes ± 30 35°
    • May erupt explosively – considered to be “most destructive”, due to eruptive style






Volcanic Domes

  • Volcanic Domes

    • Siliceous, viscous magmas (rhyolite)
    • Mt. Lassen, CA
    • Mt. St. Helens


Occurrences

  • Occurrences

    • Mid oceanic ridges (basalts)
      • Shield volcanoes in Iceland
    • Shield volcanoes over hot spots (Hawaii)
    • Composite volcanoes (subduction zones)
      • Andesitic
      • Common around Pacific Rim
    • Fissure Flows
      • Columbia River
      • Deccan Basalts, India
      • South Africa


Caldera eruptions

  • Craters, Calderas, and Vents



Hot Springs and Geysers

    • Hot Springs and Geysers




Calderas

    • Calderas
      • Large diameter (20+ km) circular depressions
      • Explosive ejection-large scale collapse
      • May contain multiple vents
      • None in Recent times
        • 10 in the last 1My
        • 3 in North America (Yellowstone, WY. and Long Valley, CA.)
          • Classified as resurgent
      • Produce large amounts of pyroclastic debris (1,000 km3)






Effects

  • Effects

    • Primary effects
    • Secondary effects
      • Debris flows
      • Mudflows
      • Floods
      • Fires


Pahoehoe

  • Pahoehoe

    • Fast moving (m/hr)
    • Low viscosity, smooth textured
  • Aa

  • Control methods

    • Bombing (most successful in Italy)
    • Chilling (most successful in Iceland
    • Deflection walls (being tried in Iceland)
    • Results have been mixed


Blowing of tephra into the atmosphere

  • Blowing of tephra into the atmosphere

  • Pyroclastic activity

  • Volcanic ash eruptions or ash falls

    • Rock fragments
    • Volcanic glass
    • Gases
  • Lateral blasts (Mt. St. Helens)

  • Pyroclastic flows or ash flows







Ash Fall

  • Ash Fall

    • Cover large areas
      • Thousands of square kilometers
    • Vegetation
    • Surface water
    • Structural damage
    • Health hazards
    • Transportation problems


Ash Flows

  • Ash Flows

    • Travel at high speeds
    • Contain very hot materials
    • Examples
      • Martinique (Pelee, and St. Pierre)
      • Mt. Unzen
      • Montserrat (Plymouth)


Gases emitted

  • Gases emitted

  • Hazardous gases seldom reach population centers

    • CO2 (hazardous)
      • Lake Nyos, Cameroon, West Africa
      • Killed 1,700 people and 3,000 cattle
  • Other gases





Debris Flows

  • Debris Flows

    • 50%+ of the particles are 2 mm or greater
    • Snow and ice melted by eruption
    • Mt. Redoubt, Alaska flow equals the Mississippi at flood stage
  • Mudflows

    • 50% of more of particles are smaller than 2 mm
  • Examples

    • Mt. Rainier's old flows threaten large cities in Washington State (Tacoma and Seattle)
    • Armero, Nevada del Ruiz, Colombia (22,000 dead)
    • Potential large "landslides" along the north coast of the Island of Hawaii may generate large tsunamis




Mount Pinatubo, Philippines

  • Mount Pinatubo, Philippines

  • Mount St. Helens, Washington

  • Pompeii Herculaneum, Italy



3 around Bay of Naples

  • 3 around Bay of Naples

  • Population density about 15,000/km2

  • Herculaneum (79 A.D); 10m ash

  • 5,000 residents, mostly escaped



Seismic activity

  • Seismic activity

  • Geophysical monitoring

  • Topographic monitoring

  • Emitted gas monitoring

  • Geologic history

  • Volcanic Alert or Warning






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