Lake Allison was a temporary lake in the

Willamette Valley The Willamette Valley ( ) is a long valley in Oregon, in the Pacific Northwest region of the United States. The Willamette River flows the entire length of the valley and is surrounded by mountains on three sides: the Cascade Range to the eas ...

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

, formed periodically by the Missoula Floods from 15,000 to 13,000 BC. The lake is the main cause of the rich and fertile soil that now characterizes the Willamette Valley.

History

Willamette Valley fertility, like the

Palouse The Palouse ( ) is a distinct geographic region of the northwestern United States, encompassing parts of north central Idaho, southeastern Washington, and, by some definitions, parts of northeast Oregon. It is a major agricultural area, primar ...

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...

, is in large part due to the largest freshwater flood scientifically documented in history. The ice floods started in Lake Missoula in

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

12,000 to 15,000 years ago during the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

and flowed down through eastern

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

, bringing fertile soil to the valley as it flowed out the

Columbia River Gorge The Columbia River Gorge is a canyon of the Columbia River in the Pacific Northwest of the United States. Up to deep, the canyon stretches for over as the river winds westward through the Cascade Range, forming the boundary between the st ...

. The narrows at

Kalama, Washington Kalama (kaw-law-maw) is a city in Cowlitz County, Washington, United States. It is part of the Longview, Washington Metropolitan Statistical Area. The population was 2,959 as of the 2020 census. Etymology James W. Phillips' ''Washington State P ...

, restricted the flow of water, causing it to back up and flood the

to a depth of above sea level as far south as Eugene.''Cataclysms on the Columbia'', by John Elliott Allen and Marjorie Burns with Sam C. Sargent, 1986. Pages 175–189. The Willamette Valley had multiple floods during the last ice age, possibly reaching 100 floods separated by centuries, to depths of 300–400 feet.''Geology of Oregon'', by Elizabeth L. Orr, William N. Orr and Ewart M. Baldwin, 1964. Pages 211–214. If floodwaters descended on the valley today, in Portland (elevation , only the tops of the West Hills, Mount Tabor,

Rocky Butte Rocky Butte (previously known as Mowich Illahee and Wiberg Butte) is an extinct cinder cone butte in Portland, Oregon, United States. It is also part of the Boring Lava Field, a group of volcanic vents and lava flows throughout Oregon and Wash ...

, Kelly Butte and Mount Scott would be visible, as would the US Bancorp Tower and the

Wells Fargo Center Wells Fargo Center may refer to: *Wells Fargo Center (Los Angeles), California *Wells Fargo Center (Sacramento), California * Wells Fargo Center (San Francisco), California * Wells Fargo Center for the Arts, Santa Rosa, California *Wells Fargo Cent ...

. Newberg’s elevation is above sea level,

Oregon City ) , image_skyline = McLoughlin House.jpg , imagesize = , image_caption = The McLoughlin House, est. 1845 , image_flag = , image_seal = Oregon City seal.png , image_map ...

, McMinnville , Salem , Corvallis and Eugene , likely rising above all of them. The lake eventually flowed out and drained, leaving of layered sedimentary soils throughout the Tualatin, Yamhill and Willamette valleys.

Name

Geologists named the lake after

Oregon State University Oregon State University (OSU) is a public land-grant, research university in Corvallis, Oregon. OSU offers more than 200 undergraduate-degree programs along with a variety of graduate and doctoral degrees. It has the 10th largest engineering ...

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 A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

) that had been transported by the floods on

iceberg An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...

s 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.

References

External links

Missoula Floods information
- Columbia River Images
Most powerful documented freshwater flood in history
- Waymark {{authority control Allison Willamette Valley Geology of Oregon Allison Willamette River

History

Name

See also

References

External links