Lake Allison
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History
Willamette Valley fertility, like the Palouse silt,[1] is in large part due to the largest freshwater flood scientifically documented[2] in history. The ice floods started in Lake Missoula in Montana 12,000 to 15,000 years ago during the Pleistocene[3] and flowed down through eastern Washington, bringing fertile soil to the valley as it flowed out the Columbia River Gorge. The narrows at Kalama, Washington, restricted the flow of water, causing it to back up and flood the Willamette Valley to a depth of Script error: No such module "convert". above sea level as far south as Eugene.[2][4][5][6] The Willamette Valley had multiple floods during the last ice age, possibly reaching 100 floods separated by centuries,[2] to depths of 300–400 feet.[6][7] If Script error: No such module "convert". floodwaters descended on the valley today, in Portland (elevation Script error: No such module "convert"., only the tops of the West Hills, Mount Tabor, Rocky Butte, Kelly Butte and Mount Scott would be visible,[7] as would the US Bancorp Tower Script error: No such module "convert". and the Wells Fargo Center Script error: No such module "convert".. Newberg’s elevation is Script error: No such module "convert". above sea level, Oregon City Script error: No such module "convert"., McMinnville Script error: No such module "convert"., Salem Script error: No such module "convert"., Corvallis Script error: No such module "convert". and Eugene Script error: No such module "convert"., likely rising above all of them. The lake eventually flowed out and drained, leaving Script error: No such module "convert". of layered sedimentary soils throughout the Tualatin, Yamhill and Willamette valleys.[1][7]
Name
Geologists named the lake after Oregon State University geologist Ira S. Allison. Among other things, he was the first person to identify and correlate Willamette silt soil in 1953 with soils at the former lake bed of Lake Lewis in eastern Washington. In the 1930s he had documented hundreds of non-native boulders (also known as glacial erratics) that had been transported by the floods on icebergs and had left a ring around the lower hills surrounding the Willamette Valley. The most notable of these is the Bellevue Erratic, off Highway 18 west of McMinnville.[6]
See also
References
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- ↑ a b Script error: No such module "citation/CS1".
- ↑ a b c Script error: No such module "citation/CS1".
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- ↑ a b c Cataclysms on the Columbia, by John Elliott Allen and Marjorie Burns with Sam C. Sargent, 1986. Pages 175–189.
- ↑ a b c Geology of Oregon, by Elizabeth L. Orr, William N. Orr and Ewart M. Baldwin, 1964. Pages 211–214.
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External links
- Missoula Floods informationScript error: No such module "Category handler".[<span title="Script error: No such module "string".">usurped]Script error: No such module "Check for unknown parameters". - Columbia River Images
- Most powerful documented freshwater flood in history - Waymark
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