Download - The Great Floods of Glacial Lakes
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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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End Moraine
Braided Stream
Steam Tunnel
Ice FaceRetreating
Glacier
Ground Moraine
What scientist think it would look like
Pre-glacial Lake Drumlin
Outwash Plain
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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
1 Purcell Lobe blocked the Clark Fork River forming Lake Missoula Channeled Scabland
2 Okanogan Lobe blocked the Columbia River (at Grand Coulee Dam) forming Glacial Lake Columbia (Grand Coulee, Banks Lake, Steamboat Rock, Dry Falls, & Moses Coulee)
3 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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PURCELL LOBE
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
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• Inundating 16,000 sq. miles hundreds of feet deep •Quickly stripped 200 feet of soil
•PURCELL LOBE
THE FIRST FRONT OF THE FLOOD
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Such catastrophic floods etched
coulees now known as the
Channeled Scablands in eastern
Washington where water velocities
were highestPURCELL LOBE
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STOPPED AT WALLULA GAP
Left scabs or erosion remnants of Basalt
PURCELL LOBE
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•Several weeks 200 cubic miles of water per day to a gap that could discharge less than 40 cubic miles per day.
PURCELL LOBE
STOPPED AT WALLULA GAP
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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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Picked apart the bedrock, and carved an immense channel system into the land
PURCELL LOBE
Missoula Floods
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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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Photo compliments of the National Park Service
Iceberg deposit (glacial erratic)
The flood ripped away huge boulders from the underlying lava rock and carried or floated them
Flood Debris
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FINAL STAGES OF THE FLOOD
•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!
Each time Lake Missoula emptied the Purcell lobe continued its
southerly progression
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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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Many layers of glacial lake sediments are found situated on top of one another; each layer represents a separate filling of the lake
Up to 40 times Flood Debris
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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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• The highest known shorelines are found at an elevation of 4,200 feet.
Ancient shorelines on Mt. JumboMissoula, MT
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13-30 feet
these ripple
marks would
dwarf any
ordinary
ripple mark
Camas Prairie ripple marks
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• 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
Photo compliments of the National Park Service
Three & one-half miles wide, Dry Falls is five times the width of Niagara Falls
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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• 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?
Okanogan Lobe
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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 <http://www.nwcreation.net/articles/evidenceoftheflood.html>
• Knapp, John. John Knapp’s Art Gallery . “Dry Falls, Washington”. July 5, 2003. <http://www.bmi.net/knapp/whitman.html>