Lake_Agassiz - Wikiparency

# Lake Agassiz **Lake Agassiz** was a vast glacial lake that formed at the southern edge of the retreating Laurentide Ice Sheet about 13,000 years ago. At its largest it was bigger than all of today's Great Lakes combined.[^mnopedia-drain] It was held in by the ice to the north and by a moraine to the south, and over its history it spread across parts of what are now [[Minnesota|Minnesota]], North Dakota, Manitoba, Ontario and Saskatchewan. The lake never covered all of this ground at once, but evidence of it is found over roughly 365,000 square miles, about five times the area of North Dakota.[^ndgs] The geologist Warren Upham named it for the Swiss-born naturalist Louis Agassiz, and described it in detail in his 1895 U.S. Geological Survey monograph, *The Glacial Lake Agassiz*.[^prairiepublic][^upham1895] The lake's flat bed is now the Red River Valley, and its remnants include Upper and Lower Red Lake and Lake of the Woods.[^dnr-lowlands] When it finally drained, about 8,200 years ago, the flood of fresh water into the North Atlantic has been linked to an abrupt cooling recorded in the Greenland ice.[^cu1999][^barber1999] On the Thury spine, Lake Agassiz is the ancestor of Minnesota's northern waters. It carved the channel of the [[Minnesota_River|Minnesota River]], made the falls that became Saint Anthony Falls, and set the stage for the floods of the [[Red_River_of_the_North|Red River of the North]]. ## Geological progression As the ice sheet melted back to the north, meltwater collected in the low ground between the ice front and higher land to the south. The ice acted as a dam, and the Big Stone Moraine blocked the lake's southern side.[^mnopedia-drain] The lake stood in North Dakota from about 11,700 years ago, and by 9,000 years ago it had retreated from the state for the last time.[^ndgs] As the ice moved and outlets opened and closed, the lake rose, fell and moved, so that its shorelines record many separate stages. ## Glacial River Warren outlet About 11,700 years ago the lake broke through the moraine near present-day Browns Valley, at the Traverse Gap, and poured south in a torrent that geologists named Glacial River Warren.[^mnopedia-drain] River Warren cut the broad valley that the much smaller Minnesota River now occupies. Where it joined the [[Mississippi_River|Mississippi River]], near what is now downtown St. Paul, it plunged over a waterfall that began retreating upstream about 12,000 years ago and became Saint Anthony Falls.[^usgs-miss] ## Phases The lake drained in stages as new outlets opened to the east and north through the thinning ice. MNopedia dates the break to the north and east, toward Hudson Bay, to about 7,400 years ago.[^mnopedia-drain] Other researchers place the final drainage of Lakes Agassiz and Ojibway through Hudson Strait at about 8,200 years ago.[^cu1999][^barber1999] When that happened, the outflow was about 15 times the present discharge of the Amazon River, and temperatures in central Greenland fell by as much as 15 °F for about 200 to 400 years.[^cu1999] ## Lakes of the Lake Agassiz basin The Minnesota DNR identifies three large lakes in the state as remnants of Glacial Lake Agassiz: Lower Red Lake, Upper Red Lake and Lake of the Woods.[^dnr-lowlands] Beyond Minnesota, the basin now drains north through the [[Red_River_of_the_North|Red River]], the [[Winnipeg_River|Winnipeg River]] and the [[Nelson_River|Nelson River]] to Hudson Bay. ## Glacial lakes draining into Lake Agassiz Lake Agassiz was one of a chain of lakes along the edge of the ice. In its last stage it was joined with glacial Lake Ojibway to the east, and the two drained together.[^cu1999] In Ontario, farmland in the Boreal Shield is found in pockets of soil formed on glacio-lacustrine deposits of proglacial Lakes Agassiz, Barlow-Ojibway and Nipissing.[^krzic] ## Formation of beaches Each time the lake held a level for long enough, waves built a shoreline of sand and gravel. These old shorelines are now known as the beach ridges.[^dnr-beach] The highest, at Herman, Minnesota, was described by Upham as "a remarkable deposit of beach gravel and sand"; lower beaches, marking later stages, pass near Norcross, Tintah and Campbell.[^mnmonthly] The ridges stand out on an otherwise level plain, and their dry, sandy and gravelly soils differ from the clays around them.[^dnr-redriver] ## Soils The lakebed is a plain of silty, sandy and clayey lake deposits. The Minnesota DNR describes the Red River Prairie as "level, uniform, and featureless, broken only by wetlands, meandering waterways, and old beach ridges."[^dnr-redriver] Farther east, in the Agassiz Lowlands, peat covers about 75% of the soils and can be more than 15 feet deep.[^dnr-lowlands] The flatness has a cost. The Red River's floodplain lies in the glacial lakebed and drops less than half a foot per mile downstream of Grand Forks; that flatness and the river's northward flow make its spring floods worse.[^usgs2005] In April 1997 the river crested at 54.35 feet at Grand Forks, against a flood stage of 28 feet, and 90% of the city's 52,000 residents were evacuated.[^mnopedia-1997] Tributaries such as the [[Red_Lake_River|Red Lake River]] cross the same flat plain, so the whole [[Drainage_basin|drainage basin]] sheds its water slowly. ## See also - [[Red_River_of_the_North]] - [[Minnesota_River]] - [[Lake_Superior]] - [[Rainy_Lake]] ## References [^mnopedia-drain]: Nelson, Paul (2025). "Draining of Glacial Lake Agassiz." *MNopedia*, Minnesota Historical Society. https://www.mnhs.org/mnopedia/search/index/event/draining-glacial-lake-agassiz [^ndgs]: Bluemle, John P. "Glacial Lake Agassiz." North Dakota Geological Survey. https://www.dmr.nd.gov/ndgs/ndnotes/agassiz/ [^prairiepublic]: Lura, Chuck (March 4, 2023). "Warren Upham & Glacial Lake Agassiz." *Natural North Dakota*, Prairie Public. https://news.prairiepublic.org/podcast/natural-north-dakota/2023-03-04/warren-upham-glacial-lake-agassiz [^upham1895]: Upham, Warren (1895). *The Glacial Lake Agassiz*. U.S. Geological Survey Monograph 25. https://doi.org/10.3133/m25 [^dnr-lowlands]: Minnesota Department of Natural Resources. "Agassiz Lowlands Subsection." https://www.dnr.state.mn.us/ecs/212Mb/index.html [^dnr-redriver]: Minnesota Department of Natural Resources. "Red River Prairie Subsection." https://www.dnr.state.mn.us/ecs/251Aa/index.html [^dnr-beach]: Minnesota Department of Natural Resources (1997). *Lake Agassiz Beach Ridges*. https://files.dnr.state.mn.us/lands_minerals/beach_ridges_coloring_book.pdf [^mnmonthly]: Rogers, Ryan. "Tracking Down Minnesota's Lost Coast." *Minnesota Monthly*. https://www.minnesotamonthly.com/travel-recreation/travel/tracking-down-minnesotas-lost-coast/ [^cu1999]: University of Colorado Boulder (July 20, 1999). "Catastrophic Draining Of Huge Lakes Tied To Ancient Global Cooling Event." https://www.colorado.edu/today/1999/07/20/catastrophic-draining-huge-lakes-tied-ancient-global-cooling-event [^barber1999]: Barber, D. C.; et al. (1999). "Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes." *Nature* 400: 344–348. https://doi.org/10.1038/22504 [^usgs-miss]: U.S. Geological Survey. "Geology – Mississippi National River and Recreation Area." https://www.usgs.gov/geology-and-ecology-of-national-parks/geology-mississippi-national-river-and-recreation-area [^usgs2005]: U.S. Geological Survey (2005). *Summary of Significant Floods in the United States and Puerto Rico, 1994 Through 1998 Water Years*. Scientific Investigations Report 2005-5194, p. 206. https://pubs.usgs.gov/sir/2005/5194/pdf/SIR20055194.4.pdf [^mnopedia-1997]: Weber, Tom (2025). "Flooding of the Red River, 1997." *MNopedia*, Minnesota Historical Society. https://www.mnhs.org/mnopedia/search/index/event/flooding-of-the-red-river-1997 [^krzic]: Krzic, Maja; Diochon, Amanda; et al. (2021). *Digging into Canadian Soils: An Introduction to Soil Science*. Boreal Shield ecozone section. ## Sources - Krzic, Maja, et al. (2021). *Digging into Canadian Soils* — on the Compendium's Northern Agriculture book shelf. ## External links - [Draining of Glacial Lake Agassiz](https://www.mnhs.org/mnopedia/search/index/event/draining-glacial-lake-agassiz), MNopedia - [The Glacial Lake Agassiz](https://pubs.usgs.gov/publication/m25) (Upham 1895), USGS Publications Warehouse  **Part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]]** — main article for section 33, *Lake Agassiz and the Red River*. Related sections: [[Hydrology]] · [[Mississippi_River]] · [[Darcy's_law]].   **Microsim — three.js (Wikitube framework):** *Lake Agassiz* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/thury/Lake_Agassiz.html" data-title="Lake Agassiz"></div> *Built from `MICROSIM_GUIDE/specs/sims/Lake_Agassiz.json`; part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]] set.*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Lake_Agassiz) : [Wikitube](https://en.wikitube.io/wiki/Lake_Agassiz) · pinned revision [1374182980](https://en.wikipedia.org/w/index.php?oldid=1374182980) · 2026-09-10 ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]]. --- *Thury main articles, wave 2 · 2026-09-10 · drafted · Compendium section 33 · sim pending THY-098.*