EART 3 Geology of National Parks 20204

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EART 3- Geology of National Parks 2/02/04

• OUTLINE
• Cascade Volcanoes- Mt. St. Helens, Crater Lake,
  Lassen Volcanic National Parks
• Orting Washington Lahar Hazard from Mt. Rainier
  Exercise- Introduction
• Mt. St. Helens Movie
• CONCEPTS
• Volcanic diversity even among stratovolcanoes
• Effects of large eruptions on society

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1980 Mt. St. Helens Eruption Sequence

• 1978 US Geological Survey recognizes that volcano
  is due to erupt soon and monitoring begins
• Spring 1980 bulge develops on north side of
  volcano- reaches 450 feet
• March 27, 1980 a large steam eruption occurs and
  area is evacuated
• May 18, 1980 832 am- A magnitude 5.1 earthquake
  triggers the bulge to break loose and slide down
  mountain- unplugging of volcanic vent initiates
  LARGE ERUPTION
• Activity continues in July 1980 and a bit through
  1982.

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Pyroclastic flow (nuee ardent) hot gas and ash
cloud that hugs mountain side and travels at
speeds up to 700 mph- DEVESTATING!!!!
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Volcanic Dome volcanic structure usually
composed of very viscous magma (rhyolite or
dacite) that is too viscous to flow and oozes out
like toothpaste.
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Trojan Nuclear Power Plant
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EART 3- Geology of National Parks 2/04/04

• OUTLINE
• Mt. St. Helens Movie
• Cascade Volcanoes- Crater Lake, Lassen Volcanic
  National Parks
• Hawaii Volcanism
• CONCEPTS
• Volcanic diversity even among stratovolcanoes

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Crater Lake created from catastorphic eruption
of Mt. Mazama 7,000 years ago
Caldera- depression resulting from collapse of
volcanic structure
Crater Lake is the deepest lake in the U.S. (over
1900 ft deep)
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Volcanic Diversity Magma composition can change
through time generating many different
compositions and therefore volcanic structures
Stratovolcanoes
Dome
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Crater Lake Rim at 8000 ft. Mt. Scott 9000
ft. Lake 5 x 6 miles
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Lassen Peak Dacite Dome- magma too viscous to
flow or explode, it oozes like toothpaste to
build a dome
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Lassen Peak-formed on the flanks of now extinct
and highly eroded stratovolcano (Mt. Tehama) as a
later stage of volcanic activity
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SW
NE
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Hot Springs
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Lassen Peak Recent Volcanic Activity
Pyroclastic deposits and lava flows erupted in
1915
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Lassen Peak Recent Volcanic Activity
Pyroclastic deposits and lava flows erupted from
1914-1921
1984
1926
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