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











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.



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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