Purcell Lobe blocked the Clark Fork River forming Lake Missoula Channeled Scabland


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Purcell Lobe blocked the Clark Fork River forming Lake Missoula Channeled Scabland

  • 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







Created Glacial Lake Missoula

  • Created Glacial Lake Missoula

  • Covering 7,800 square kilometers

  • PURCELL LOBE



Ice dam, merely a small section of the lobe

  • 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



2nd Burst through the Clark Fork Canyon

  • 2nd Burst through the Clark Fork Canyon

  • Ten times combined flow of all the rivers of the world



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









Creates Lake Allison which filled the Willamette Valley all the way to Eugene

  • 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



1250 feet at Wallula Gap

  • 1250 feet at Wallula Gap

  • 1000 feet at Dalles

  • 925 feet at Hood River

  • 400 Feet at Portland

  • 275 feet at Clatskanie











West Bar, along the Columbia River near Quincy, exhibits “mega-ripples” -- ripples generated by the massive flood

  • West Bar, along the Columbia River near Quincy, exhibits “mega-ripples” -- ripples generated by the massive flood



















Lake Columbia --

  • Lake Columbia --

        • across Spokane
  • Cut deep canyons, or coulees in bedrock









15,000 y.a.

  • 15,000 y.a.

  • Olympic Mountains help squeeze the ice sheet down the Puget Lowlands

  • 1 mile thick

  • Gouged/Scarred Puget Sound lowlands



13, 500 y.a. receded

  • 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




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