Glacial Lake Columbia was the lake formed on the ice-dammed Columbia River behind the Okanogan lobe of the Cordilleran Ice Sheet when the lobe covered of the

Waterville Plateau Waterville may refer to: Places Canada * Waterville, Quebec * Waterville, Nova Scotia * Waterville, Carleton County, New Brunswick, a rural community * Waterville, Sunbury County, New Brunswick, a rural community * Waterville, Newfoundland and La ...

west of Grand Coulee in central

Washington state Washington (), officially the State of Washington, is a U.S. state, state in the Northwestern United States, Pacific Northwest region of the Western United States. Named for George Washington—the first President of the United States, U.S. p ...

during the Wisconsin glaciation.The Wisconsin glaciation began about 80,000 years ago and ended around 10,000 years ago. Lake Columbia was a substantially larger version of the modern-day lake behind the

Grand Coulee Dam Grand Coulee Dam is a concrete gravity dam on the Columbia River in the U.S. state of Washington, built to produce hydroelectric power and provide irrigation water. Constructed between 1933 and 1942, Grand Coulee originally had two powerho ...

. Lake Columbia's overflow – the diverted Columbia River – drained first through Foster Coulee, and as the ice dam grew, through first Moses Coulee, and finally, the Grand Coulee.

Glacial Lake Missoula

The Cordilleran ice sheet also blocked the Clark Fork River and created Glacial Lake Missoula, rising behind a high ice dam in flooded valleys of western Montana. Over 2000 years the ice dam periodically failed, releasing approximately 40 high-volume Missoula Floods of water down the Columbia River drainage, passing through glacial Lake Columbia. The largest flood is estimated to be the initial flood at 2,500 km³ (600 mi³), with subsequent floods occurring at roughly 20 to 80 year intervals. Since Lake Columbia was impounded behind the Okanogan lobe, which rose to , this lobe effectively blocked the normal course of the Columbia River, blocking the Missoula Floods and diverting water to flow across much of eastern Washington state. The erosion from the floods created the Grand Coulee as well as the Dry Falls,

Palouse Falls Palouse Falls is a waterfall on the Palouse River, about upstream of the confluence with the Snake River in southeast Washington, United States. The falls are in height. The falls consist of an upper fall with a drop around , which lies north ...

, and the Channeled Scablands features of eastern Washington state.

Flood deposits

Flood beds on the Sanpoil arm of glacial Lake Columbia show episodic flood deposits as well as deposit grading and rhythmical repetition. Since Glacial Lake Columbia remained filled between Missoula floods, annual deposits ( varves) can be observed between the Missoula flood deposits, they help to establish the periodicity of these major floods. The flood deposits can be distinguished from annually-deposited varves by both their thickness and the presence of materials foreign to the immediate drainage. Atwater reports from 35 to 55 annual varves between flood deposits in Lake Columbia, supporting a period of 35 to 55 years between ice dam failures.

References

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Columbia Columbia may refer to: * Columbia (personification), the historical female national personification of the United States, and a poetic name for America Places North America Natural features * Columbia Plateau, a geologic and geographic region i ...

Geology of Washington (state)