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| Former lakes of the United States | |
|---|---|
| Name | Former lakes of the United States |
| Caption | Reconstruction of Lake Bonneville extent |
| Location | United States |
| Type | historical |
Former lakes of the United States
Former lakes of the United States encompass natural basins and palaeolakes that once occupied parts of North America, now drained, desiccated, or converted into other landforms by geologic, climatic, or anthropogenic processes. These bodies, ranging from enormous Pleistocene reservoirs like Lake Agassiz and Lake Bonneville to smaller riverine oxbows and reclaimed Great Salt Lake-precursor basins, illuminate interactions among glaciation, tectonics, ancient hydrology, indigenous occupation, and modern engineering projects. Study of these former lakes draws on evidence from United States Geological Survey, National Oceanic and Atmospheric Administration, and academic institutions such as University of Utah and University of Minnesota.
"Former lakes" denotes basins that held standing water for sustained intervals but no longer do so at comparable extent. Criteria include sedimentary deposits, strandlines, and geomorphic markers documented by United States Geological Survey, American Geophysical Union, and regional geological surveys like the Utah Geological Survey. Related concepts include palaeolakes, terminal basins, and proglacial lakes exemplified by Lake Missoula, Glacial Lake Agassiz, and Lake Lahontan. Distinguishing former lakes from ephemeral floodplains involves stratigraphic analysis, radiocarbon dating at centers such as Woods Hole Oceanographic Institution and isotope studies conducted in collaboration with institutions like Smithsonian Institution.
The Pleistocene epoch produced some of the largest former lakes in the contiguous United States. Lake Bonneville, a pluvial lake on the Bonneville Salt Flats and in the Great Basin, left shorelines visible near Devils Hole and in formations studied by National Park Service researchers. Lake Lahontan covered much of present-day Nevada with remnants such as Pyramid Lake and Walker Lake. In the northern plains, Lake Agassiz—bounded by ice sheets associated with the Cordilleran Ice Sheet and Laurentide Ice Sheet—influenced outlets to the Hudson Bay and produced spillways into the Mississippi River system. Catastrophic drainage events such as the Missoula Floods carved the Channeled Scablands and deposited features across Washington State and Idaho, with geomorphology analyzed by researchers at University of Washington and Washington State University.
Many former lakes were bounded by ice dams that failed during deglaciation. Glacial Lake Missoula and Glacial Lake Columbia drained repeatedly, generating megafloods recorded by J Harlen Bretz's studies and later confirmed with support from Carnegie Institution for Science analyses. Other glacially influenced features include Lake Agassiz’s complex drainage history tied to the retreat of the Laurentide Ice Sheet and outlets like the St. Lawrence River corridor. In alpine regions, ice-marginal lakes in the Rocky Mountains and Sierra Nevada left lacustrine terraces and varve sequences studied by National Science Foundation-funded teams and regional universities.
Anthropogenic activities have eliminated or transformed lakes across the United States. Diversions tied to projects by the U.S. Bureau of Reclamation and Army Corps of Engineers created reservoirs such as Lake Mead while reducing flows into downstream basins, affecting former lakebeds like the Salton Sea (formed in association with Colorado River diversions) and seasonal wetlands of the Central Valley altered by California State Water Project. Draining for agriculture converted prairie potholes in Iowa and Minnesota and former oxbow lakes along the Mississippi River into farmland under policies shaped by agencies including the Natural Resources Conservation Service.
Loss of lacustrine habitats has cascading effects on regional ecology and water resources. Decline of wetlands and terminal lakes influences migratory routes used by species cataloged by Audubon Society and alters saline basins such as those once feeding the Great Salt Lake. Groundwater recharge dynamics change in basins formerly hosting persistent lakes, with implications for management by United States Geological Survey hydrologists and policy makers in agencies like the Environmental Protection Agency. Paleolimnological cores from former lake sediments provide records of climate proxies utilized by researchers at Paleoecology Laboratory programs and climate centers including NOAA Paleoclimatology.
Former lakes preserve archaeological sites, trade routes, and cultural landscapes important to indigenous nations such as the Shoshone, Ute, Lakota, and Ojibwe. Exposed lakebeds reveal artifacts, canoe remains, and stratified settlements informing work by institutions like the Smithsonian Institution and university archaeology departments at University of California, Berkeley and Harvard University. Cartographic records from explorers such as John C. Frémont and ethnographic studies by scholars associated with Bureau of American Ethnology contextualize human adaptations to lakeshore environments now lost or transformed.
- Pacific Northwest: Glacial Lake Missoula and the Channeled Scablands across Washington and Idaho, studied by J Harlen Bretz and modern geomorphologists at University of Montana. - Intermountain West: Lake Bonneville, Lake Lahontan, remnants like Pyramid Lake and Walker Lake, with basin research from University of Utah. - Northern Plains: Lake Agassiz and proglacial lakes influencing Minnesota, North Dakota, and Manitoba landscapes examined by University of North Dakota and University of Minnesota. - Southwest: historic changes to Salton Sea, Lake Cahuilla reconstructions tied to Colorado River dynamics and documented by California Department of Water Resources. - Great Lakes fringe and inland: palaeolakes such as Glacial Lake Chicago and precursor bodies to Lake Michigan and Lake Erie researched by the Great Lakes Environmental Research Laboratory. - Southeast and Midwest: drained oxbows and prairie potholes across Iowa, Illinois, and Mississippi River floodplains with conservation implications for organizations including The Nature Conservancy.