The Great Flood: A Geologic Event Which Shaped Salem

Salem is located at the confluence of Mill Creek and the Willamette River. Since its settlement in the 1840’s the city has grown north and east onto the flat valley floor and expanded south and west into the Salem and Eola Hills.Twelve thousand years ago horses, camels, mammoths, bison, deer, bear, panthers, tigers, and lions roamed the valley. Thousands of birds, including giant condors, hawks, eagles, geese, and ducks, nested in the area. (Allen, page 86.)

The natural environment of the Salem area changed with the coming of what is known today as the “Bretz Flood” or the “Lake Missoula Floods.” Scientists estimate that the area sustained approximately forty such floods. The source of the flooding was a river in northern Idaho, blocked by glacial dams. When the river broke through the dams, it generated a wall of water estimated to be 200 feet tall. The flood roared across eastern Washington releasing approximately twice the energy of the meteorite that destroyed the era of the dinosaurs.

Scientists believe the flood would have been visible from space.

The largest and last of the floods formed the major geologic features of the Willamette Valley including the rich deposits of alluvial soils. Today the cities of Eugene, Albany, Woodburn, and Salem occupy the level valley floor and area farmers prize the region’s rich soil. 

It is believed that the last great flood held the equivalent of eight times the energy released when Mount Mazama (Crater Lake) exploded. Other comparisons estimate it released 800 times the energy of the Mount Saint Helens eruption or 375 times the energy released in the 1906 San Francisco earthquake (Allen, page 200.)

Evidence of the flood still exists in the Salem area. An erratic boulder carried into the valley by an iceberg is located near Sheridan, Oregon. Another of these boulders has been placed on the campus of Willamette University in Salem. 

It is believed that flood waters (in what is now Salem) crested approximately 400 feet above current sea level. Using today’s landmarks, “lake front property” would have been available in the vicinity of Hilfiker Lane and Sunridge, Argyle, and Eastlake Drives in South Salem as well as Sunwood Drive, Burley Road, Upper Breckenridge Loop, and the grounds of West Salem High School in West Salem. It is believed that the intersection of State and Commercial Streets in downtown Salem was under 243 feet of water.

Scientists have studied the great floods for many years. Geologist Thomas Condon postulated a “Willamette Sound” in 1871 and J. Harlan Bretz was the first geologist to describe the “Spokane Flood” in 1919. Yet another scientist, Ira S. Allison, identified major features of the flooding throughout the Willamette Valley, adding to the evidence of this great geologic event of the recent past. It is also said that the Kalapuyas’ native legends include a description of a “water beast” which once roamed the valley floor.

Researched and written by Rodney R. Stubbs. Edited by Kyle Jansson..

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Bibliography:

Allen, J.E., and Marjorie Burns. Cataclysms on the Columbia.  Portland, Oregon: Timber Press, 1986.

Mellville, Jacobs. Kalapuya Ethnologic Texts, Seattle: University of Washington, 1945.

Shaded Relief Map. Washington, D.C.: United States Geologic Service (USGS.)

This article originally appeared on the original Salem Online History site and has not been updated since 2006.