Lake Agassiz

Lake Agassiz was an immense glacial lake located in the center of North America. Fed by glacial runoff at the end of the last glacial period, its area was larger than all of the present-day Great Lakes combined.

Conception

First postulated in 1823 by William Keating, it was named after Louis Agassiz in 1879 after he was the first to realize it was formed by glacial action.

Geological progression

Geologists have come to a consensus on the likely geological progression of Lake Agassiz.

Forming around 13,000 calendar years before present (almost 12,000 ¹⁴C years before present), the lake came to cover much of Manitoba, western Ontario, northern Minnesota, eastern North Dakota, and Saskatchewan. At its greatest extent, it may have covered as much as 440,000 square kilometers, larger than any currently existing lake in the world (including the Caspian Sea). This is roughly the size of Iraq, the 58th largest country in the world, and larger than California, the third largest U.S. state, but smaller than the Yukon, the ninth largest Canadian territory or province.

The lake drained at various times south through the Traverse Gap into Glacial River Warren (parent to the Minnesota River, a tributary of the Mississippi River), into the Great Lakes, or west through the Yukon Territory and Alaska. Climatologists believe that a major outbreak of Lake Agassiz in about 11000 BC drained through the Great Lakes and Saint Lawrence River into the Atlantic Ocean. This may be the cause of the Younger Dryas stadial. A return of the ice for some time offered a reprieve, and after retreating north of the Canadian border about 9,900 years ago it refilled. These events had significant impact on climate, sea level and possible early human civilization.

Much of the final drainage of Lake Agassiz may have occurred in a very short time—perhaps as little as one year. A recent study by Turney and Brown links this rapid drainage and subsequent global sea level rise of about one meter to the expansion of agriculture in Europe; he suggests that this may also account for various flood myths of prehistoric cultures, including the biblical flood. [Turney, C.S.M. and Brown, H. (2007) "Catastrophic early Holocene sea level rise, human migration and the Neolithic transition in Europe." "Quaternary Science Reviews", 26, 2036-2041; [http://www.eurekalert.org/pub_releases/2007-11/uoe-fk111507.php "The Mother of All Floods?] November 21, 2007.]

The last major shift in drainage occurred about 8,400 calendar years before present (about 7,700 ¹⁴C years before present), when the lake took up its current watershed, draining into Hudson Bay. The lake drained nearly completely over the next 1,000 years or so, leaving behind Lake Winnipeg, Lake Winnipegosis, Lake Manitoba, and Lake of the Woods, among others. The outlines and volumes of these lakes are still slowly changing due to differential isostatic rebound.

Other geological and geomorphological evidence for Lake Agassiz can also be seen today. Raised beaches, many kilometers from any water, mark the former boundaries of the lake at various times. Several modern river valleys, including the Red River, the Assiniboine River and the Minnesota River, were originally cut by water entering or leaving the lake. The fertile soils of the Red River Valley agricultural region are Lake Agassiz silt.

ee also

*Glacial River Warren
*Glacial history of Minnesota
*Proglacial lakes of Minnesota

References

Notes

ources

Books, journals and monographs

* cite journal
last = Fisher
first = Timothy G.
authorlink =
coauthors =
title = River Warren boulders, Minnesota, USA: catastrophic paleoflow indicators in the southern spillway of glacial Lake Agassiz
journal = Boreas
volume = 33
issue = 4
pages = 349–58
publisher = Taylor & Francis
date = December, 2004
url = http://www.eeescience.utoledo.edu/Faculty/Fisher/Fisher%20-%20River%20Warren%20boulders,%20Minnesota,%20USA%20-%20catastrophic%20paleoflow%20indicators%20in%20the%20southern%20spillway%20of%20glacial%20Lake%20Agassiz.pdf
doi = 10.1080/0300948041001938
id = ISSN 0300-9483
accessdate = 2007-09-22
*cite journal |last=Hostetler |first=S. W. |authorlink= |coauthors="et al." |year=2000 |month= |title=Simulated influences of Lake Agassiz on the climate of central North America 11,000 years ago |journal=Nature |volume=405 |issue=6784 |pages=334–337 |doi=10.1038/35012581 |url= |accessdate= |quote=
* Citation
last = Ojakangas
first = Richard W.
author-link =
last2 = Matsch
first2 = Charles L
author2-link =
title = Minnesota's Geology
place= Minneapolis
publisher = University of Minnesota Press
year = 1982
location =
volume =
edition =
url =
doi =
id = ISBN 0-8166-0953-5
* cite journal
last = Perkins
first = S.
authorlink =
coauthors =
title = Once Upon a Lake
journal = Science News
volume = 162
issue = 18
pages = 283
date = 2002
doi = 10.2307/4014064 Abstract at cite web
url = http://cgrg.geog.uvic.ca/abstracts/PerkinsOnceDuring.html
title = Bibliography of Canadian Geomorphology
publisher = Canadian Geomorphology Research Group
accessdate = 2007-12-15
* Pielou, E. C. (1991). "After the Ice Age: The Return of Life to Glaciated North America", Chicago: University of Chicago Press, ISBN 0-2266-6812-6
* Citation
last = Sansome
first = Constance Jefferson
authorlink =
coauthors =
title = Minnesota Underfoot: A Field Guide to the State's Outstanding Geologic Features
publisher = Voyageur Press
date = 1983
location = Stillwater, MN
pages =
url =
doi =
id = ISBN 0-8965-8036-9
* cite journal
last = Upham
first = Warren
authorlink =
coauthors =
title = The Glacial Lake Agassiz
journal = Monographs of the United States Geological Survey
volume = XXV
issue =
pages =
publisher = United States Geological Survey/University of North Dakota
date = 1896/2002
url = http://www.lib.ndsu.nodak.edu/govdocs/text/lakeagassiz/
doi =
id =
accessdate = 2007-09-22

Websites

*cite web
last = Boswell
first = Randy
date = 2007-11-19
url = http://www.canada.com/topics/technology/story.html?id=ffaed9c2-2e55-4555-b01e-2d7b60f8371e&k=39290
title = Noah's Ark flood spurred European farming
publisher = CanWest News Service
accessdate = 2007-11-22
*cite web
last = Lusardi
first = B. A.
date = 1997
url = http://www.winona.edu/geology/MRW/MNglance/Mn_Quaternary.pdf
title = Quaternary Glacial Geology
work = Minnesota at a Glance
publisher = Minnesota Geological Survey, University of Minnesota
accessdate = 2007-09-22
*cite web
date = 2004-11-15
url = http://mrbdc.mnsu.edu/mnbasin/fact_sheets/valley_formation.html
title = Valley Formation
work = Fact Sheets
publisher = Minnesota River Basin Data Center (MRBDC, Minnesota State University, Mankato
accessdate = 2007-09-22

External links

* cite map
publisher= Minnesota Department of Natural Resources
title= Glacial Lake Agassiz
url= http://www.dnr.state.mn.us/rprp/claycounty/lakeagassiz.html
edition=
section=
accessdate=2007-09-22

* cite url
publisher= Natural Resources Canada
title= Beach ridges of former Glacial Lake Agassiz, northwestern Manitoba
url= http://gsc.nrcan.gc.ca/landscapes/details_e.php?photoID=480
edition=
section=
accessdate=2008-09-02