Lake Lewis was a temporary lake in the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Thou ...

region of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

, largely formed by the

Missoula Floods The Missoula floods (also known as the Spokane floods or the Bretz floods or Bretz's floods) were cataclysmic glacial lake outburst floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the las ...

in about the 14th millennium B.C. Lake Lewis was formed when the restricted flow of waters from periodic cataclysmic floods from

Glacial 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 Mic ...

, pluvial

Lake Bonneville Lake Bonneville was the largest Late Pleistocene paleolake in the Great Basin of western North America. It was a pluvial lake that formed in response to an increase in precipitation and a decrease in evaporation as a result of cooler temperature ...

, and perhaps from subglacial outbursts, backed up through the constriction formed by the

Wallula Gap Wallula Gap () is a large water gap of the Columbia River in the northwest United States in southeast Washington. It cuts through the Horse Heaven Hills basalt anticlines in the Columbia River Basin, just south of the confluence of the Wa ...

in the

Horse Heaven Hills The Horse Heaven Hills are a long range of high, rolling hills in Klickitat, Yakima, and Benton counties in Washington. The hills are an anticline ridge in the Yakima Fold Belt formed by north–south compression of lava flows in the Columbi ...

(southern

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 ...

). Water also backed up further downstream on the

Columbia River The Columbia River ( Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia ...

between

and

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 ...

, delaying the drainage of Lake Lewis. The water remained for a period of weeks before the flood waters drained through Wallula Gap, just southeast of the Tri-Cities area. Lake Lewis reached an elevation of about above sea level (today's sea level) before subsiding. Lake Lewis also flooded the Yakima, Walla Walla,

Touchet Touchet is a surname, and may refer to: Members of the English peerage: * James Touchet, 5th Baron Audley, (c. 1398–1459) * George Thicknesse-Touchet, 19th Baron Audley (1758–1818) ** George Thicknesse-Touchet, 20th Baron Audley, (1783–1837) ...

and Tucannon river valleys.

Evidence for Lake Lewis

Wallula Gap

Wallula Gap is a large

water gap A water gap is a gap that flowing water has carved through a mountain range or mountain ridge and that still carries water today. Such gaps that no longer carry water currents are called wind gaps. Water gaps and wind gaps often offer a prac ...

through basalt

anticline In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is t ...

s in the

basin just south of the confluence of the

Walla Walla River The Walla Walla River is a tributary of the Columbia River, joining the Columbia just above Wallula Gap in southeastern Washington in the United States. The river flows through Umatilla County, Oregon, and Walla Walla County, Washington. Its drai ...

and the Columbia River. The Wallula Gap, which has existed for many millions of years, was widened by the historic flow of the Salmon-Snake and Columbia Rivers combined with the glacial waters that poured across the

Channeled Scablands The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods ...

during the Missoula Floods. The Wallula Gap constrained the flow such that less than 1/5 of the 800 km³ of water per day entering could be discharged. As a result, the floods filled the Pasco Basin and formed, for a short period, Lake Lewis. The large volumes of flood water passing through the gap contributed substantially to the erosion of the gap, as is evidenced by the shear walls and of scab-features such as the "Sisters."

Touchet Formation

Lake Lewis backflooded into the Yakima, Walla Walla,

and Tucannon River Valleys. In these relatively calm arms of the lake, the slackwaters were thick with suspended materials eroded from the scablands above. Some of the suspended materials settled out, creating thick Touchet Formation layers which are found throughout these valleys.

Glacial erratics

The maximum elevation of the flood, as established by other indications, is confirmed by

glacial erratic A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by glacial ice, often over distances of hundred ...

s, which were stranded on the slopes of the

and other elevated regions in the mid-Columbia at elevations of up to above sea level. There were several long ridges (Saddle Mountains, Frenchman Hills, and Rattlesnake Mountain) that were above flood level. Peaks like the Badger, Candy, and Red Mountains were islands.Northwest Science & Technology, Spring 2004 Issue
At this level, much of the Columbia Basin would have been submerged.

References

External links

* * {{authority control Lewis, Lake Lewis, Lake Lewis Geology of Washington (state)