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

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

• Creates/defines Straits of Juan de Fuca
• Cascades on east
• Olympics and Vancouver Island west

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