Glacial Lake Missoula

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Glacial Lake Missoula
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The Setting

• 15,000 ybp
• End of last Ice Age
• Canada, U.S locked in deep freeze
• Ice sheets had crept southward
• Coastline 300 ft lower

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Causes of Lake Missoula

• Advancing ice blocked many rivers
• Clark Fork River in Montana
• Ice dam created Lake Missoula

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Glacial Lake Missoula
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Glacial Lake Missoula

• Enough water to create a lake 1 mile wide and 1
  mile deep from Portland to San Francisco (650
  miles)
• Bigger than Lake Erie and Ontario combined

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Picture This

• The Ice Dam broke
• GLM emptied in 48 hrs. !!
• Covered four states

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How Much Water!!

• Combine ALL the rivers of the world into one
  super river, GLM released 10xs that much water
• Columbia River was 4,000xs the size it is today

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The NW landscape was changed

• Soil was stripped from E. WA
• Huge boulders or erratics were moved
• Gorge was widened
• Portland was under 400 ft. of H2O

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Dry Falls, Washington

• The rush of the water created huge canyons as
  well as impressive waterfalls
• Dry Falls would have dwarfed Niagara during the
  floods

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Just Once?

• This happened multiple times, possibly 25, as the
  ice would then advance and create another dam
• Soil deposited in slow moving water

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Bellevue Erratic

• Does this rock look familiar?
• It is 5 minutes outside of Mac
• Huge rock rafted into the Willamette Valley
  entombed in ice during the floods

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Hard To Believe

• It took a great deal of time for geologists to
  accept the idea of these cataclysmic floods
• Nothing of this magnitude had ever been reported

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