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Lake Agassiz
by James Bergseid
Physical Geology
Spring 2007

Lake Agassiz


Formed by an ancient glacier sheet, that no longer exists, and that covered much of North America, was Lake Agassiz. Lake Agassiz is an ancient lake that also no longer exists: so why is it so important?




When you take a look at all of the Great Lakes that remain between the U.S. and Canada today, keeping their immensities in mind, Lake Agassiz was larger than all the Great Lakes combined. If it existed today Agassiz would be the largest lake in the world surpassing even the expansiveness of the Caspian Sea. According to Perkins, “During the waning days of the ice age, North America’s Lake Agassiz was the largest body of fresh water in the world. At times it held more water than that in all the world’s lakes today” (Perkins).

Lake Agassiz was located over much of what is today Manitoba, western Ontario, Saskatchewan, nothern Minnesota and northern North Dakota. This lake formed approximately 13,000 years ago. This Pleistocene lake was able to be, because the glacier that melted, and the lake that subsequently formed, was landlocked for a time. The glacier itself created a major depression in the vast area it covered.   Lake Agassiz, in  effect, was one great kettle lake.

          This ancient lake, though gone, may have affected mankind for thousands of years; it definitely has created some of the best soil conditions in the world for agriculturists today. It is believed that around about 11,000 B.C, Lake
Agassiz had a mass drainage through Hudson Bay, St. Lawrence River and the Minnesota River (which drains into the Mississippi River). This may have been the cause of an event known as Younger Dryas. Sea levels rose greatly thus changing earth’s climate. There was a brief, yet “big freeze” that occurred as a direct result to Lake Agassiz’s contribution to the Atlantic Ocean. This freeze affected North America and Europe mostly. During the freeze, Lake Agassiz was able to accumulate ice in its basin, and it refilled about 9,900 years ago. The last major modification to the lake happened nearly 8,400 years ago: the lake drained for approximately 1,000 years out through the Hudson and other aforementioned waterways. All that remains of Lake Agassiz, now, is Lake Winnepeg, Lake Winnipegosis, Lake Manitoba, Lake of the Woods, the Red River and many other smaller lakes and rivers in the Minnesota/Canadian border area. This exportation of mass amounts of water back into the ocean may have been what is now depicted as the great flood of biblical times. Perkins relays in his article, “During Lake Agassiz’ demise, a young civilization may have inhabited ground that is now the floor of the Persian Gulf…The Tigris and Euphrates Rivers, which now meet the Persian Gulf at the Iraqi shoreline, then flowed another 1,000 km across the flat, dry basin before they reached the sea. Even modest changes in the sea level from the final drainage of Lake Agassiz half a world away would have forced people who lived beside those rivers to flee their flooded lands” (Perkins). 




Today, the Red River Valley rests at the bottom of the ancient lake. The glacial till, including fine silt rested at the bottom of Lake Agassiz, especially at the southern most finger of the extinct lake that is the Red River Valley. The fine silt, over thousands of years mixed in with the clays in the soil. As the glacier stretched southward, it pulverized rocks along the way. There is a fine mix mineral from the many types of pulverized rocks that is included in the topsoils of Eastern North Dakota and Western Minnesota. The minerals and silt rest in the soil at this location due to moraines left by the glacier and the elevated, ancient beaches left by Lake Agassiz in the Red River



Diagram of glacial plucking and abrasion 

(Image depicts glacial ice flowing and plucking and pulverizing rock via glacial abrasion.) Image found at Author: Original: Lmb at es.wikipedia Vectorized version: Chabacano. Permission granted by Luis María Benítez at Wikipedia en espanol project.


The area where the lake used to lie is the second largest wetland in the world. It is second only to the Everglades of Florida. The wetlands left by Lake Agassiz are peatlands. Peatlands are areas where the topsoil is heavily infiltrated and thoroughly mixed with decayed or decaying plant matter. According to Barry Ray of FSU News, “Peatlands represent one of the largest carbon stores on the planet. Since the end of the last ice age some 18,000 years ago, approximately 900 trillion pounds of carbon dioxide have been transferred from the atmosphere to the organic soils of peatlands around the world.” This raises questions about what may happen if these gases are released. “We want to know if this landform is still actively growing and absorbing carbon, or if climatic conditions have been altered to the point where the mass is wasting away and decomposing. Peatland decomposition will result in both carbon dioxide and methane being released into the atmosphere and will serve as a positive feedback to enhance further climate change” (Ray).

The importance of Lake Agassiz may exist in the theory of the biblical great flood of early humans in Persia. The importance of Agassiz’ fertile valleys is important to the agricultural industries of the U.S. and Canada. The study of global warming can greatly benefit from the study of the peatlands that remain at the bottom of the lost, great kettle lake.


Works Cited


Perkins, S. Once Upon A Lake. Science News Issue: 162(18) Found on CGRG Bibliography of Canadian Geomorphology Search Results website here: <>


Ray, Berry. FSU Researchers to Study Effects of Climate Change in Minnesota Peatlands. FSU News at Florida State University, Tallahassee, FL. 2007. Found at < >


Upham, Warren. The Glacial Lake Agassiz. Washington Government Printing Office 1895. Monographs of the United States Geological Survey Volume XXV. Washington Government Printing Office 1896. As Scanned and formatted by Kathryn Thomas North Dakota State University Libraries April 30, 2002. Found at <>


Wikipedia, the free encyclopedia. “Lake Agassiz”. <> 2007.