The Great Floods of Glacial Lakes
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Transcript of The Great Floods of Glacial Lakes
The Great Floods of Glacial Lakes
Colonnades of Columbia Plateau basalt.
Rocks cascading into a lake left by a glacierin the
Canadian Rockies
CORDILLERAN ICE SHEET - GLACIAL MISSOULA & COLUMBIA LAKES
• Cordilleran Ice Sheet -- 4000 feet thick
End Moraine
Braided Stream
Steam Tunnel
Ice FaceRetreating
Glacier
Ground Moraine
What scientist think it would look like
Pre-glacial Lake Drumlin
Outwash Plain
How Glaciers Move
• Large rocks (till) at the base of a glacier that have been plucked from the terrain as the ice moved over it.
The Cordilleran Ice Sheet south into northern Washington, Idaho, and Montana
MISSOULA & COLUMBIA LAKES
• Ice Age 15,000 and 12,800 y.a.
• Near end of the Pleistocene Epoch
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
PURCELL LOBE ICE DAM
•Blocked Clark Fork River •(Idaho-Montana border)
• Created Glacial Lake Missoula
• Covering 7,800 square kilometers
(western Montana)PURCELL LOBE
PURCELL LOBE ICE DAM
Contained more water than Lakes Erie & Ontario combined
• Held 2,000 square km. of water
• Approximately 600 meters deep
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
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
2nd Burst through the Clark Fork
Canyon
• Ten times combined flow of all
the rivers of the world
PURCELL LOBE
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
• Inundating 16,000 sq. miles hundreds of feet deep •Quickly stripped 200 feet of soil
•PURCELL LOBE
THE FIRST FRONT OF THE FLOOD
Such catastrophic floods etched
coulees now known as the
Channeled Scablands in eastern
Washington where water velocities
were highestPURCELL LOBE
STOPPED AT WALLULA GAP
Left scabs or erosion remnants of Basalt
PURCELL LOBE
•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
STOPPED AT
WALLULA GAP
• Water filled the Pasco basin, Yakima and Touchet Valleys forming temporary Lake Lewis
• PURCELL LOBE
FINAL STAGES OF THE FLOOD
The torrent widened and deepened the Columbia River Gorge, baring the
majestic cliffs seen today
PURCELL LOBE
• Pushed back and reversed the flow of the
Snake River all the way past Lewiston,
Idaho.
PURCELL LOBE
• Temporary lakes formed in the Scablands
and silt, sand, and gravel settled out of the
water.
PURCELL LOBE
• Channeled Scablands
• The very dark areas• = lakes and rivers
Picked apart the bedrock, and carved an immense channel system into the land
PURCELL LOBE
Missoula Floods
Where did all the loess, dirt, sand, gravel and silt end up?
Some of the material were deposited in the Willamette Valley in Oregon
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
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
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
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
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
Looking at the evidence
Ancient shorelines on Mt. Jumbo
Missoula, MT
• The highest known shorelines are found at an elevation of 4,200 feet.
Ancient shorelines on Mt. JumboMissoula, MT
13-30 feet
these ripple
marks would
dwarf any
ordinary
ripple mark
Camas Prairie ripple marks
• Lake Columbia -- – across Spokane
• Cut deep canyons, or coulees in bedrock
• 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
DRY FALLSby John Knapp http://www.bmi.net/knapp/whitman.html
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
OKANOGAN LOBE
• Soap Lake today is known as Dry Falls
• Skeleton of one of the greatest waterfalls
Okanogan Lobe
OKANOGAN LOBE
Dry Falls is 3.5 miles wide with a drop of over 400 ft.
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
Grand Coulee
• 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
PUGET LOBE
• The Puget Lobe from the Glacier -
• Seattle under a mile of ice
• Glacier left marks on both the– Cascade and Olympic mountain ranges.
PUGET LOBE
• 15,000 y.a.
• 1 mile thick
• Gouged/Scarred Puget Sound lowlands – Cascades on east– Olympics and Vancouver Island west
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
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.
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>