The%20Great%20Floods%20of%20Glacial%20Lakes

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The Great Floods of Glacial Lakes
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Colonnades of Columbia Plateau basalt.
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Rocks cascading into a lake left by a glacierin
the Canadian Rockies
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CORDILLERAN ICE SHEET - GLACIAL MISSOULA
COLUMBIA LAKES

• Cordilleran Ice Sheet -- 4000 feet thick

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How Glaciers Move
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• Large rocks (till) at the base of a glacier that
  have been plucked from the terrain as the ice
  moved over it.

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The Cordilleran Ice Sheet south into northern
Washington, Idaho, and Montana MISSOULA
COLUMBIA LAKES
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• Ice Age 15,000 and 12,800 y.a.
• Near end of the Pleistocene Epoch

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CORDILLERAN ICE SHEET LOBES

• Purcell Lobe blocked the Clark Fork River forming
  Lake Missoula Channeled Scabland
• Okanogan Lobe blocked the Columbia River (at
  Grand Coulee Dam) forming Glacial Lake Columbia
  (Grand Coulee, Banks Lake, Steamboat Rock, Dry
  Falls, Moses Coulee)
• The Puget Lobe scoured the Puget Sound

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PURCELL LOBE ICE DAM

• Blocked Clark Fork River
• (Idaho-Montana border)

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• Created Glacial Lake Missoula
• Covering 7,800 square kilometers
• (western Montana)
• PURCELL LOBE

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• PURCELL LOBE ICE DAM
• Contained more water than Lakes Erie Ontario
  combined
• Held 2,000 square km. of water
• Approximately 600 meters deep

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• 1st Lake Missoula floated the Ice Dam
• Ice dam, merely a small section of the lobe
• three miles long
• ten miles across
• 2,000 feet tall

PURCELL LOBE
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1st Lake Missoula floated the Ice Dam

• When the water behind the dam became deep enough
• southern finger of the vast ice sheet
• popped up like ice cubes in a glass of lemonade

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• 2nd Burst through the Clark Fork Canyon
• Ten times combined flow of all the rivers of the
  world

PURCELL LOBE
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THE FIRST FRONT OF THE FLOOD

• Mass of water, debris, and ice 2,000 feet high
• Raced toward the ocean at 65 miles per hour

PURCELL LOBE
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THE FIRST FRONT OF THE FLOOD

• Inundating 16,000 sq. miles hundreds of feet
  deep
• Quickly stripped 200 feet of soil
• PURCELL LOBE

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• Such catastrophic floods etched coulees now known
  as the Channeled Scablands in eastern Washington
  where water velocities were highest

PURCELL LOBE
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STOPPED AT WALLULA GAP
Left scabs or erosion remnants of
Basalt PURCELL LOBE
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STOPPED AT WALLULA GAP

• Several weeks 200 cubic miles of water per day to
  a gap that could discharge less than 40 cubic
  miles per day.
• PURCELL LOBE

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STOPPED AT WALLULA GAP

• Water filled the Pasco basin, Yakima and Touchet
  Valleys forming temporary Lake Lewis
• PURCELL LOBE

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FINAL STAGES OF THE FLOOD
The torrent widened and deepened the Columbia
River Gorge, baring the majestic cliffs seen
today PURCELL LOBE
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• Pushed back and reversed the flow of the Snake
  River all the way past Lewiston, Idaho.

PURCELL LOBE
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• Temporary lakes formed in the Scablands and silt,
  sand, and gravel settled out of the water.

PURCELL LOBE
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• Channeled Scablands
• The very dark areas
• lakes and rivers

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Missoula Floods

Picked apart the bedrock, and carved an immense
channel system into the land PURCELL LOBE
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Where did all the loess, dirt, sand, gravel and
silt end up? Some of the material were
deposited in the Willamette Valley in Oregon
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Flood Debris
Iceberg deposit (glacial erratic)
The flood ripped away huge boulders from the
underlying lava rock and carried or floated them
Photo compliments of the National Park Service
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FINAL STAGES OF THE FLOOD
Each time Lake Missoula emptied the Purcell lobe
continued its southerly progression

• Formed a new dam
• Causing the lake to refill
• Resulting in a new flood
• Average of every 55 years or so for 2,000 years!

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FINAL STAGES OF THE FLOOD

• Piles of rocks left behind near Eugene were
  brought by icebergs broken off the original ice
  dam formed by the Purcell lobe of the Cordilleran
  Ice Sheet

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Flood Debris
Up to 40 times
Many layers of glacial lake sediments are found
situated on top of one another each layer
represents a separate filling of the lake
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FINAL STAGES OF THE FLOOD

• Not far from the present day site of Portland,
  the river makes two 90 degree turns.
• Ice and debris formed a temporary dam causing the
  floodwaters to spill into the Willamette Valley
  as far south as present day Eugene

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Looking at the evidence
Ancient shorelines on Mt. Jumbo Missoula, MT
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Ancient shorelines on Mt. JumboMissoula, MT

• The highest known shorelines are found at an
  elevation of 4,200 feet.

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Camas Prairie ripple marks
13-30 feet these ripple marks would dwarf any
ordinary ripple mark
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OKANOGAN LOBE

• Lake Columbia --
• across Spokane
• Cut deep canyons, or coulees in bedrock

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• Coulee south of Coulee City.
• Unlike the Grand Canyon, which was eroded by a
  river, the coulees of Washington were carved out
  by Ice Age floods.

Okanogan Lobe
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DRY FALLSby John Knapp
http//www.bmi.net/knapp/whitman.html
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Dry FallsEastern Washington
Three one-half miles wide, Dry Falls is five
times the width of Niagara Falls
Photo compliments of the National Park Service
Okanogan Lobe
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OKANOGAN LOBE

• Soap Lake today is known as Dry Falls
• Skeleton of one of the greatest waterfalls

Okanogan Lobe
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OKANOGAN LOBE
Dry Falls is 3.5 miles wide with a drop of over
400 ft.
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OKANOGAN LOBE

• Two Major North South Grand Coulees
• Larger Upper Coulee -a river over an 800 ft.
  waterfall 4 miles Wide 20 miles Long
• Lower Coulee is 7 m long and about 1 mile
  wide
• Eroding power took pieces of Basalt rock causing
  the falls to retreat 20 miles and self-destruct
• (where Grand Coulee Dam is today)

Okanogan Lobe
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Grand Coulee
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Okanogan Lobe

• This is a view below and down the channel at
• Palouse Falls.
• Can you imagine the amount of water it took to
  carve out this canyon?

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PUGET LOBE
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• The Puget Lobe from the Glacier -
• Seattle under a mile of ice
• Glacier left marks on both the
• Cascade and Olympic mountain ranges.

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PUGET LOBE

• 15,000 y.a.
• 1 mile thick
• Gouged/Scarred Puget Sound lowlands
• Cascades on east
• Olympics and Vancouver Island west

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Puget Lobe

• 13, 500 y.a. receded
• Melting snow/ice water runoff
• Caused
• Pacific Ocean to rise
• Flooded Puget Sound Trough
• irregular coastline
• Numerous islands

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Bibliography

• Alt, David. Glacial Lake Missoula and Its
  Humongous Floods. Mountain Press Publishing
  Company, 2003.
• Alt, David and Donald W. Hyndman. Northwest
  Exposures A Geologic Story of the Northwest.
  Mountain Press Publishing Company, 1995.

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Bibliography

• Durr, Gerald. Evidence of the Flood in Franklin
  County. July 17, 2003 lthttp//www.nwcreation.net/a
  rticles/evidenceoftheflood.htmlgt
• Knapp, John. John Knapps Art Gallery . Dry
  Falls, Washington. July 5, 2003.
  lthttp//www.bmi.net/knapp/whitman.htmlgt