Lake Allison was a temporary lake in the

Willamette Valley The Willamette Valley ( ) is a 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 east, the ...

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

, 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 geographic region of the northwestern United States, encompassing parts of North Central Idaho, north central Idaho, southeastern Washington (part of eastern Washington), and by some definitions, parts of northeast Oregon. ...

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 (chemistry), suspension with water. Silt usually ...

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

Lake Missoula Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago. The lake measured about and contained about of water, half the volume of Lake Mi ...

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

12,000 to 15,000 years ago during the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

and flowed down through eastern Washington, 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 state ...

. The narrows at

Kalama, Washington Kalama () 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 Place Nam ...

, 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 Mount Tabor ( ; ; ), sometimes spelled Mount Thabor, is a large hill of biblical significance in Lower Galilee, Northern District (Israel), northern Israel, at the eastern end of the Jezreel Valley, west of the Sea of Galilee. In the Hebrew Bi ...

, Rocky Butte, Kelly Butte and Mount Scott would be visible, as would the US Bancorp Tower and the Wells Fargo Center . Newberg’s elevation is above sea level, Oregon City , 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 university, public Land-grant university, land-grant research university in Corvallis, Oregon, United States. OSU offers more than 200 undergraduate degree programs and a variety of graduate and doctor ...

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 erratic is a glacially deposited rock (geology), rock differing from the type of country rock (geology), rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by gla ...

) that had been transported by the floods on

iceberg An iceberg is a piece of fresh water ice more than long that has broken off a glacier or an ice shelf and is floating freely in open water. Smaller chunks of floating glacially derived ice are called "growlers" or "bergy bits". Much of an i ...

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

* - 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