Glacial Lake Columbia (west) and Glacial Lake Missoula (east) are shown south of the Cordilleran ice sheet. The areas inundated in the Columbia and Missoula floods are shown in red.
Cause
Ice dam ruptures
Meteorological history
Duration
Between 15,000 and 13,000 years ago
Flood
Overall effects
Areas affected
The current states of: Idaho, Washington, and Oregon
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 last ice age. These floods were the result of periodic sudden ruptures of the ice dam on the Clark Fork River that created Glacial Lake Missoula. After each ice dam rupture, the waters of the lake would rush down the Clark Fork and the Columbia River, flooding much of eastern Washington and the Willamette Valley in western Oregon. After the lake drained, the ice would reform, creating Glacial Lake Missoula again.
These floods have been researched since the 1920s. During the last deglaciation that followed the end of the Last Glacial Maximum, geologists estimate that a cycle of flooding and reformation of the lake lasted an average of 55 years and that the floods occurred several times over the 2,000-year period between 15,000 and 13,000 years ago. U.S. Geological Survey hydrologist Jim O'Connor and Spain's Museo Nacional de Ciencias Naturales scientist Gerardo Benito have found evidence of at least twenty-five massive floods, the largest discharging about 10 cubic kilometers per hour (2.7 million m³/s, 13 times that of the Amazon River).[1][2] Alternate estimates for the peak flow rate of the largest flood range up to 17 cubic kilometers per hour.[3] The maximum flow speed approached 36 meters/second (130 km/h or 80 mph).[3]
Within the Columbia River drainage basin, detailed investigation of the Missoula floods' glaciofluvial deposits, informally known as the Hanford formation, has documented the presence of Middle and Early Pleistocene Missoula flood deposits within the Othello Channels, Columbia River Gorge, Channeled Scabland, Quincy Basin, Pasco Basin, and the Walla Walla Valley. Based on the presence of multiple interglacial calcretes interbedded with flood deposits, magnetostratigraphy, optically stimulated luminescence dating, and unconformity truncated clastic dikes, it has been estimated that the oldest of the Pleistocene Missoula floods happened before 1.5 million years ago. Because of the fragmentary nature of older glaciofluvial deposits, which have been largely removed by subsequent Missoula floods, within the Hanford formation, the exact number of older Missoula floods, which are known as ancient cataclysmic floods, that occurred during the Pleistocene cannot be estimated with any confidence.[4][5]
^"Science writer Richard Hill gives a brief geologic history of the Columbia River Gorge". The Oregonian. Archived from the original on 2008-08-04. Retrieved 2008-06-15.
^Lehnigk, KE; Larsen, IJ (2022). "Pleistocene megaflood discharge in Grand Coulee, Channeled Scabland, USA". Journal of Geophysical Research: Earth Surface. 127 (1): e2021JF006135. Bibcode:2022JGRF..12706135L. doi:10.1029/2021JF006135. S2CID 245545657.
^ abBjornstad, Bruce N. (c. 2006). On the trail of the Ice Age floods: a geological field guide to the mid-Columbia basin / Bruce Bjornstad. Sandpoint, Idaho: Keokee Books. p. 2. ISBN 978-1-879628-27-4.
^Medley, E. (2012) Ancient Cataclysmic Floods in the Pacific Northwest: Ancestors to the Missoula Floods. Unpublished Masters thesis, Portland State University, Portland, Oregon. 174 pp.
^Spencer, P. K., and M. A. Jaffee (2002) Pre-Late Wisconsinan Glacial Outburst Floods in Southeastern Washington—The Indirect Record. Washington Geology. vol. 30, no. 1/2, pp. 9–16.
The Missoulafloods (also known as the Spokane floods or the Bretz floods or Bretz's floods) were cataclysmic glacial lake outburst floods that swept periodically...
occurred. The periodic rupturing of the ice dam resulted in the MissoulaFloods – cataclysmic floods that swept across eastern Washington and down the Columbia...
outburst floods were caused by the collapse of either ice sheets or glaciers that formed the dams of proglacial lakes. Examples of older outburst floods are...
Sisters". During the Missoulafloods, water backed up in the Pasco Basin because of the narrow opening of the Wallula Gap. The floods were so large in volume...
Snake River. Unlike the MissoulaFloods, which also occurred during the same period in the Pacific Northwest, the Bonneville flood happened only once. It...
outburst floods were the result of periodic sudden ruptures of ice dams like those triggering the Missoulafloods. In the US, large glacial outburst floods have...
geologist, best known for his research that led to the acceptance of the MissoulaFloods and for his work on caves. Bretz was born on 2 September 1882, in the...
approximately 40 high-volume MissoulaFloods of water down the Columbia River drainage, passing through glacial Lake Columbia. The largest flood is estimated to be...
after the 1920s, with the new understanding about the MissoulaFloods, one of the largest floods documented, caused by the collapse of an ice barrier during...
interpretation of the geological consequences of the Glacial Lake Missoulafloods of the last glacial period that occurred about 18,000 to 15,000 years...
audience the cataclysmic glacial MissoulaFloods through articles and his book Glacial Lake Missoula and Its Humongous Floods (Mountain Press, 2001. ISBN 978-0878424153)...
define the progression of the MissoulaFloods, which occurred around 18,400 to 15,700 calendar years ago. During the floods, flow through the Wallula Gap...
Coulee, a formerly dry coulee near the Columbia River, formed by the MissoulaFloods during the Pleistocene epoch. Grand Coulee Dam, built by the United...
the rivers of the world. Because such ice dams can re-form, these MissoulaFloods happened at least 59 times, carving Dry Falls below Grand Coulee. In...
believed that the eastern side of the lake was in the path of the ancient MissoulaFloods. The lake sits at the south end of the Purcell Trench, carved by glaciers...
lake in the Willamette Valley of Oregon, formed periodically by the MissoulaFloods from 15,000 to 13,000 BC. The lake is the main cause of the rich and...
erosion, the river's drainage basin was significantly modified by the MissoulaFloods at the end of the most recent ice age. Humans began living in the watershed...
MissoulaFloods, which occurred during the same period, the Bonneville Flood happened only once. The flood is believed to be the second largest flood...
growing region was severely impacted by the immense water flows of the Missoulafloods. The scouring effect of the waters stripped the top soils down to the...
Scablands – Landscape in eastern Washington state scoured by cataclysmic floods during the Pleistocene epoch Grand Coulee – Ancient river bed in the U.S...
Missoula & its Humongous Floods. Mountain Press Publishing Company. ISBN 0-87842-415-6. Bjornstad, Bruce (2006). On the Trail of the Ice Age Floods:...
Missoula & its Humongous Floods. Mountain Press Publishing Company. ISBN 0-87842-415-6. Bjornstad, Bruce (2006). On the Trail of the Ice Age Floods:...
the discharge of the Amazon River and ten times as much as the MissoulaFloods. This flood would have descended a relatively gentle ramp into the Mediterranean...
larger floods. Events from Salmon Glacier near Hyder have damaged roads near the Salmon River. Immense prehistoric GLOFs, known as the MissoulaFloods or...
000 years ago at the end of a hanging valley, and was created by the Missoulafloods. According to the creation story from the Multnomah tribe (from whom...
the Pacific Northwest region of North America, formed by periodic MissoulaFloods along the Columbia River paleocourse between 21,000 and 16,000 years...
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