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The Great Floods of Glacial Lakes. Colonnades of Columbia Plateau basalt.

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Presentation on theme: "The Great Floods of Glacial Lakes. Colonnades of Columbia Plateau basalt."— Presentation transcript:

1 The Great Floods of Glacial Lakes

2 Colonnades of Columbia Plateau basalt.


4 Rocks cascading into a lake left by a glacier in the Canadian Rockies

5 CORDILLERAN ICE SHEET - GLACIAL MISSOULA & COLUMBIA LAKES Cordilleran Ice Sheet -- 4000 feet thick

6 End Moraine Braided Stream Steam Tunnel Ice Face Retreating Glacier Ground Moraine What scientist think it would look like Pre-glacial Lake Drumlin Outwash Plain

7 How Glaciers Move

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

9 The Cordilleran Ice Sheet south into northern Washington, Idaho, and Montana MISSOULA & COLUMBIA LAKES

10 Ice Age 15,000 and 12,800 y.a. Near end of the Pleistocene Epoch

11 CORDILLERAN ICE SHEET LOBES 1Purcell Lobe blocked the Clark Fork River forming Lake Missoula Channeled Scabland 2Okanogan 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


13 PURCELL LOBE ICE DAM Blocked Clark Fork River (Idaho-Montana border)

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

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

16 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

17 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

18 2nd Burst through the Clark Fork Canyon Ten times combined flow of all the rivers of the world PURCELL LOBE

19 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

20 Inundating 16,000 sq. miles hundreds of feet deep Quickly stripped 200 feet of soil PURCELL LOBE THE FIRST FRONT OF THE FLOOD

21 Such catastrophic floods etched coulees now known as the Channeled S cablands in eastern Washington where water velocities were highest PURCELL LOBE

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

23 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

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

25 FINAL STAGES OF THE FLOOD The torrent widened and deepened the Columbia River Gorge, baring the majestic cliffs seen today PURCELL LOBE


27 P ushed back and reversed the flow of the Snake River all the way past Lewiston, Idaho. PURCELL LOBE

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

29 Channeled Scablands The very dark areas = lakes and rivers

30 Picked apart the bedrock, and carved an immense channel system into the land PURCELL LOBE Missoula Floods

31 Where did all the loess, dirt, sand, gravel and silt end up? Some of the material were deposited in the Willamette Valley in Oregon

32 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


34 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

35 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

36 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

37 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

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

39 The highest known shorelines are found at an elevation of 4,200 feet. Ancient shorelines on Mt. Jumbo Missoula, MT

40 13-30 feet these ripple marks would dwarf any ordinary ripple mark Camas Prairie ripple marks

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

42 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

43 DRY FALLS by John Knapp

44 Dry Falls Eastern 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

45 OKANOGAN LOBE Soap Lake today is known as Dry Falls Skeleton of one of the greatest waterfalls Okanogan Lobe

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

47 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

48 Grand Coulee

49 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


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

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

53 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

54 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.

55 Bibliography Durr, Gerald. Evidence of the Flood in Franklin County. July 17, 2003 Knapp, John. John Knapp’s Art Gallery. “Dry Falls, Washington”. July 5, 2003.

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