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Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick

Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick. Flood Routes (basalt lava or water). CORDILLERAN ICE SHEET LOBES. Purcell Lobe blocked the Clark Fork River forming Lake Missoula Channeled Scabland

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Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick

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  1. Cordilleran Ice Sheet 15-20,000 years ago – 4000 feet thick

  2. Flood Routes (basalt lava or water)

  3. 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

  4. PURCELL LOBE ICE DAM • Blocked Clark Fork River • (Idaho-Montana border)

  5. Created Glacial Lake Missoula • Covering 7,800 square kilometers PURCELL LOBE

  6. Ice dam, merely a small section of the lobe • three miles long • ten miles across (broad and flat) • 2,000 feet tall – thus holding back 2000 feet of hydraulic head which EVENTUALLY Burst through the Clark Fork Canyon • Ten times combined flow of all the riversof the world PURCELL LOBE

  7. 2nd Burst through the Clark Fork Canyon • Ten times combined flow of all the rivers of the world PURCELL LOBE

  8. Such catastrophic floods etched coulees now known as the Channeled Scablandsin eastern Washington where water velocities were highest – average velocity was 65 mph. “Constricted Burst velocities” in excess of 100 mph  instantaneous erosion. PURCELL LOBE

  9. First Effects of Flood • Inundating 16,000 sq. miles hundreds of feet deep • Quickly stripped 200 feet of soil • Left scabs or erosion remnants of Basalt • STOPPED AT WALLULA GAP (constriction point) – creates Lake Lewis • Several weeks 200 cubic miles of water per day (pressure in) to a gap that could discharge less than 40 cubic miles per day (pressure out). Velocity increases by square root of 5

  10. Wallula Gap

  11. Kalama (WA) Constriction (Carrolls Bluffs)

  12. Restriction at Kalama • Creates Lake Allison which filled the Willamette Valley all the way to Eugene • Estimated depth was 380 feet at Eugene • Flood waters delivered most of the silt to produce the most fertile agricultural soils in the country

  13. Estimate Flood Levels • 1250 feet at Wallula Gap • 1000 feet at Dalles • 925 feet at Hood River • 400 Feet at Portland • 275 feet at Clatskanie

  14. The Draining of Glacial Lake Missoula

  15. THE GREAT COULEES OF CENTRAL WASHINGTON Coulees are gouged-out canyons in the high desert of central Washington that now carry little or no flowing water. The two most spectacular are Moses Coulee and, just to the east, Grand Coulee. Both photos are of Grand Coulee and show the region known as Dry Falls. During the height of the Ice Age Floods, a torrent of water plucked the basalt bedrock away, forming a waterfall 400 feet tall and 3.5 miles wide. (Niagara Falls, in comparison, measures one-mile wide, with a 165-foot drop.)

  16. This is an area near Sprague Lake that shows pool formations that remain today as evidence of the great lakes flow across this area.

  17. West Bar, along the Columbia River near Quincy, exhibits “mega-ripples” -- ripples generated by the massive flood Dramatic evidence remains First Noticed by Harlen Bretz in 1922 and published in 1923. Bretz was not warmly received as the scientific community hates catastrophism

  18. Erosion Feature

  19. FINAL STAGES OF THE FLOOD

  20. Flood Debris The flood ripped away huge boulders from the underlying lava rock and carried or floated them – constriction points literally “shoot” these rocks out Photo compliments of the National Park Service

  21. Columbia Gorge significantly deepened by flood The Dalles constriction point makes Lake Condon Kalama Narrows back up floods Willamette Valley

  22. 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! Each Flood event 2-3 weeks

  23. Ancient shorelines on Mt. JumboMissoula, MT • The highest known shorelines are found at an elevation of 4,200 feet.

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

  25. Lake Columbia -- • across Spokane • Cut deep canyons, or coulees in bedrock OKANOGAN LOBE

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

  27. Palouse Falls Canyon Carved out over 2000 year period Okanogan Lobe

  28. PUGET LOBE

  29. PUGET LOBE • 15,000 y.a. • Olympic Mountains help squeeze the ice sheet down the Puget Lowlands • 1 mile thick • Gouged/Scarred Puget Sound lowlands • Creates/defines Straits of Juan de Fuca • Cascades on east • Olympics and Vancouver Island west

  30. Puget Lobe • 13, 500 y.a. receded • Melting snow/ice = water runoff • Caused • Pacific Ocean to rise • Flooded Puget Sound Trough • North South Hills (Drumlins) in Seattle • Created very irregular coastline • Numerous islands remain

  31. Mt. Erie (WA)

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