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The Laurentide Ice Sheet
Laurentide Ice Sheet
was a massive sheet of ice that covered millions of square kilometers, including most of Canada
Canada
and a large portion of the northern United States, multiple times during the Quaternary
Quaternary
glacial epochs— from 2.588 ± 0.005 million years ago to the present.[1] The last advance covered most of northern North America between c. 95,000 and c. 20,000 years before the present day, and among other geomorphological effects, gouged out the five Great Lakes and the hosts of smaller lakes of the Canadian shield. These lakes extend from the eastern Northwest Territories, through most of northern Canada, and the upper Midwestern United States
United States
(Minnesota, Wisconsin, and Michigan) to the Finger Lakes, through Lake Champlain and Lake George areas of New York, across the northern Appalachians into and through all of New England
New England
and Nova Scotia. At times, the ice sheet's southern margin included the present-day sites of northeastern coastal towns and cities such as Portsmouth, New Hampshire, Boston, New York City, and Great Lakes
Great Lakes
coastal cities and towns as far south as Chicago
Chicago
and St. Louis, Missouri—and then followed quite precisely the present course of the Missouri River
Missouri River
up to the northern slopes of the Cypress Hills, beyond which it merged with the Cordilleran Ice Sheet. The ice coverage extended approximately as far south as 38 degrees latitude in the mid-continent.[2]

Contents

1 Description 2 Ice Centers

2.1 Cordilleran Ice Flow 2.2 Keewatin Ice Flow 2.3 Labrador
Labrador
Ice Flow 2.4 Baffin Ice Flow

3 See also 4 References 5 Further reading 6 External links

Description[edit]

The maximum extent of glacial ice in the north polar area during the Pleistocene
Pleistocene
period included the vast Laurentide ice sheet in eastern North America.

This ice sheet was the primary feature of the Pleistocene
Pleistocene
epoch in North America, commonly referred to as the ice age. It was up to 2 mi (3.2 km) thick in Nunavik, Quebec, Canada
Canada
but much thinner at its edges where nunataks were common in hilly areas. It created much of the surface geology of southern Canada
Canada
and the northern United States, leaving behind glacially scoured valleys, moraines, eskers and glacial till. It also caused many changes to the shape, size, and drainage of the Great Lakes. As but one of many examples, near the end of the last ice age, Lake Iroquois extended well beyond the boundaries of present-day Lake Ontario, and drained down the Hudson River
Hudson River
into the Atlantic Ocean.[3] Its cycles of growth and melting were a decisive influence on global climate during its existence. This is because it served to divert the jet stream which would otherwise flow from the relatively warm Pacific Ocean through Montana
Montana
and Minnesota
Minnesota
to the south. This gave the southwestern United States, otherwise a desert, abundant rainfall during ice ages — in extreme contrast to most other parts of the world which became exceedingly dry, though the effect of ice sheets in Europe
Europe
had an analogous effect on the rainfall in Afghanistan, parts of Iran, possibly western Pakistan
Pakistan
in winter, as well as North Africa.

The Barnes Ice Cap, containing remnants of the Laurentide Ice Sheet.

Its melting also caused major disruptions to the global climate cycle, because the huge influx of low-salinity water into the Arctic Ocean via the Mackenzie River[4] is believed to have disrupted the formation of North Atlantic Deep Water, the very saline, cold, deep water that flows from the Greenland Sea. This interrupted the thermohaline circulation, creating the brief Younger Dryas
Younger Dryas
cold epoch and a temporary re-advance of the ice sheet,[5] which did not retreat from Nunavik
Nunavik
until 6,500 years ago. Some people[who?] have argued that huge influxes of fresh water stopped the feeding of the ice sheet and starved it, aiding the retreat that had already begun. This is a controversial position because it is known that the North Atlantic was very cold throughout glacial periods and it is likely that the anticyclone on top of the ice sheet helped sustain it through moist easterly winds which encouraged snow-bearing winds from the south.[citation needed] During the Pre-Illinoian Stage the Laurentide Ice Sheet
Laurentide Ice Sheet
extended even farther south, advancing as far as the Missouri and Ohio River valleys. The ultimate collapse of the Laurentide Ice Sheet
Laurentide Ice Sheet
is also suspected to have influenced European agriculture indirectly through the rise of global sea levels. Canada's oldest ice is a 20,000-year-old remnant of the Laurentide Ice Sheet called the Barnes Ice Cap, located on central Baffin Island. Ice Centers[edit] During the Late Pleistocene, the Laurentide ice sheet reached from the Rocky Mountains
Rocky Mountains
eastward through the Great Lakes, into New England, covering nearly all of Canada
Canada
east of the Rocky Mountains.[6] Three major ice centers formed in North America: the Labrador, Keewatin, and Cordilleran. The Cordilleran covered the region from the Pacific Ocean to the eastern front of the Rocky Mountains
Rocky Mountains
and the Labrador
Labrador
and Keewatin fields are referred to as the Laurentide Ice Sheet. Central North America has evidence of the numerous lobes and sublobes. The Keewatin ice covered the western interior plains of North America from the Mackenzie River
Mackenzie River
to the Missouri River
Missouri River
and the upper reaches of the Mississippi River. The Labrador
Labrador
ice covered spread over eastern Canada and the northeastern part of the United States
United States
abutting the Keewatin lobe in the western Great Lakes
Great Lakes
and Mississippi valley.[6] Cordilleran Ice Flow[edit] Cordilleran Ice Sheet
Cordilleran Ice Sheet
covered up to 2,500,000 square kilometres (970,000 sq mi) at the Last Glacial
Glacial
Maximum. The eastern edge abutted the Laurentide ice sheet. The sheet was anchored in the Coast Mountains
Coast Mountains
of British Columbia
British Columbia
and Alberta, south into the Cascade Range
Cascade Range
of Washington. This is one and a half times the water held in the Antarctic. Anchored in the mountain backbone of the west coast, the ice sheet dissipated north of the Alaska Range
Alaska Range
where the air was too dry to form glaciers.[6] It is believed that the Cordilleran ice melted rapidly, in less than four thousand years. The water created numerous Proglacial lake
Proglacial lake
along the margins; i.e., Lake Missoula, often leading to catastrophic floods as with the Missoula Floods. Much of the topography of Eastern Washington
Eastern Washington
and northern Montana
Montana
and North Dakota
North Dakota
was affected.[6] Keewatin Ice Flow[edit] Keewatin Ice flow has had four or five primary lobes identified ice divides extending from a dome over west-central Keewatin. Two of the lobes abut the adjacent Labrador
Labrador
and Baffin ice sheets. The primary lobes flow (1) towards Manitoba
Manitoba
and Saskatchewan; (2) toward Hudson Bay; (3) towards the Gulf of Boothia, and (4) towards the Beaufort Sea.[7] Labrador
Labrador
Ice Flow[edit] Ice flowed across all of Maine
Maine
and into the Gulf of St. Lawrence, completely covering the Maritime Provinces. The Appalachian Ice Complex, flowed from the Gaspé Peninsula
Gaspé Peninsula
over New Brunswick, the Magdalen Shelf, and Nova Scotia.[7] The Labrador
Labrador
flow extended across the mouth of the St. Lawrence River, reaching the Gaspé Peninsula
Gaspé Peninsula
and across Chaleur Bay. From the Escuminac center on the Magdalen Shelf, flowed onto the Acadian Peninsula
Acadian Peninsula
of New Brunswick
New Brunswick
and southeastward, onto the Gaspe, burying the western end of Prince Edward Island
Prince Edward Island
and reached the head of Bay of Fundy. From the Gaspereau center, on the divide crossing New Brunswick
New Brunswick
flowed into the Bay of Fundy
Bay of Fundy
and Chaleur Bay.[7] Baffin Ice Flow[edit] The Baffin Ice Flow was circular and centered over the Foxe Basin. A major divide across the basin, created a westward flow across the Melville Peninsula, from an eastward flow over Baffin Island
Baffin Island
and Southampton Island. Across southern Baffin Island, two divides created four additional lobes. The Penny Ice Divide split the Cumberland Peninsula, where Pangnirtung
Pangnirtung
created flow toward Home Bay on the north and Cumberland Sound
Cumberland Sound
on the south. The Amadjuak Ice Divide on the Hall Peninsula, where Iqaluit
Iqaluit
sits created a north flow into Cumberland Sound and a south flow into the Hudson Strait. A secondary Hall Ice Divide formed a link to a local ice cap on the Hall Peninsula. The current ice caps on the Baffin Island
Baffin Island
is thought to be a remnant from this time period, although it was not a part of the Baffin Ice Flow, but an autonomous flow.[7] See also[edit]

Canadian Shield Glacial
Glacial
history of Minnesota Lake Agassiz Wisconsin
Wisconsin
glaciation

References[edit]

^ Cohen, K.M.; Finney, S.C.; Gibbard, P.L.; Fan, J.-X. "International Chronostratigraphic Chart 2013" (PDF). http://www.stratigraphy.org/icschart/chronostratchart2013-01.pdf. ICS. Retrieved 15 June 2014.  External link in website= (help) ^ Dyke, A.S.; Prest, V.K. (1987). "Late Wisconsinan and Holocene History of the Laurentide Ice Sheet". Géographie physique et Quaternaire. 41 (2): 237–263.  ^ Flint, R.F. 1971. Glacial
Glacial
and Quaternary
Quaternary
Geology. Wiley and Sons, NY. 892 p. ^ Murton, J.B.; Bateman, M.D.; Dallimore, S.R; Teller, J.T.; Yang, Z. (2010). "Identification of Younger Dryas
Younger Dryas
outburst flood path from Lake Agassiz to the Arctic Ocean". Nature. 464 (7289): 740–743. Bibcode:2010Natur.464..740M. doi:10.1038/nature08954. PMID 20360738.  ^ Broecker, W.S.; Denton, G.H. (1989). "The role of ocean-atmosphere reorganizations in glacial cycles". Geochimica et Cosmochimica Acta. 53 (10): 2465–2501. Bibcode:1989GeCoA..53.2465B. doi:10.1016/0016-7037(89)90123-3.  ^ a b c d Geologic Framework and Glaciation of the Central Area, 1-1-2006; Christopher L. Hill; Boise State University, Boise, Idaho; 2006 ^ a b c d Late Wisconsinan and Holocene History of the Laurentide Ice Sheet, 10.7202/032681ar; Arthur S. Dyke, Victor K. Prest; Geological Survey of Canada; Ottawa, Ontario; 1987; http://id.erudit.org/iderudit/032681ar

Further reading[edit]

"Noah's Flood Kick-started European Farming?". University of Exeter. Retrieved 2007-11-20. 

External links[edit]

The Retreat of Glaciers in North America (MPEG-Video)

v t e

Continental glaciations

General

Canadian Shield Glacial
Glacial
history of Minnesota Lake Agassiz Lake Chicago Lake Tight Last Glacial
Glacial
Maximum Laurentide Ice Sheet List of prehistoric lakes Post-glacial rebound Proglacial lake Teays River Timeline of glaciation

Landforms

Erosional

Fjord Glacial
Glacial
striae Ribbon lake Roche moutonnée Tunnel valley U-shaped valley

Depositional

Drumlin Drumlin
Drumlin
field Erratic block Moraine Pulju moraine Rogen moraine Terminal moraine Till plain Veiki moraine

Glacifluvial

Diluvium Esker Giant current ripples Kame Kame
Kame
delta Kettle hole Outwash fan Sandur

North American places

Canada

Arrowhead Provincial Park, Ontario Big Rock (glacial erratic), Alberta Cypress Hills (Canada), Saskatchewan Eramosa River, Ontario Eskers
Eskers
Provincial Park, British Columbia Foothills Erratics Train, Alberta Lion's Head Provincial Park, Ontario Origin of the Oak Ridges Moraine, Ontario Ovayok Territorial Park, Nunavut

United States

Chippewa Moraine
Moraine
State Recreation Area, Wisconsin Coteau des Prairies, South Dakota Devil's Lake State Park, Wisconsin Glacial
Glacial
Lake Wisconsin, Wisconsin Glacial
Glacial
Lakes State Park, Minnesota Horicon Marsh
Horicon Marsh
State Wildlife Area, Wisconsin Ice Age Floods National Geologic Trail, Idaho, Oregon & Washington Ice Age National Scientific Reserve, Wisconsin Ice Age Trail, Wisconsin Interstate State Park, Minnesota
Minnesota
& Wisconsin Kelleys Island, Ohio Kettle Moraine
Moraine
State Forest, Wisconsin Lake Bonneville, Utah Lake Lahontan, Nevada Lake Missoula, Montana Mill Bluff State Park, Wisconsin Oneida Lake, New York Two Creeks Buried Forest State Natural Area, Wisconsin Withrow Moraine
Moraine
and Jameson Lake Drumlin
Drumlin
Field, Washington Yosemite National Park, California

Eurasian and Antarctic
Antarctic
places

Antarctica Hardangerfjord Killary Harbour Lambert Glacier Monte Rosa Ross Ice Shelf Svalbard

Time periods

Illinoian Stage Interglacial Interstadial Last glacial period Little Ice Age Older Dryas Pleistocene Pre-Illinoian Stage Quaternary
Quaternary
glaciation Sangamonian Stage Wisconsin
Wisconsin
glaciation Younger Dryas

Category

v t e

Pleistocene
Pleistocene
proglacial lakes and related seas

Africa

Lake Makgadikgadi

Asia

West Siberian Glacial
Glacial
Lake Lake Tengger

Europe

Ancylus Lake Baltic Ice Lake Lake Harrison Lake Komi Lake Lapworth Lake Pickering Littorina Sea Mastogloia Sea Yoldia Sea

North America

Nelson River
Nelson River
drainage

Proglacial lakes of Minnesota Lake Agassiz Lake Bassano Lake Souris

James Bay
James Bay
drainage

Lake Ojibway Tyrrell Sea

Great Lakes

Lake Admiralty Lake Algonquin
Lake Algonquin
(Multiple basins) Lake Arkona Lake Chicago Lake Chippewa Lake Duluth Early Lake Erie Lake Frontenac Lake Houghton (glacial) Glacial
Glacial
Lake Iroquois Lake Lundy Lake Dana Mackinac Falls Lake Maumee Lake Minong Nipissing Great Lakes
Great Lakes
(Multiple basins) Early Lake Ontario Lake Saginaw Lake Stanley Lake Tonawanda Lake Warren Lake Wayne Lake Whittlesey Champlain Sea

Columbia River
Columbia River
system

Lake Bonneville Glacial
Glacial
Lake Columbia Lake Lahontan Lake Missoula

Puget Sound
Puget Sound
system

Glacial
Glacial
Lake Russell Glacial
Glacial
Lake Hood Lake Nisqually Lake Puyallup Glacial
Glacial
Lake Sammamish Lake Skokomish

Upper Missouri River

Lake Cut Bank Lake Chouteau Lake Great Falls Lake Circle Lake Jordan (Montana) Lake Musselshell Lake Glendive Lake McKenzie

Upper Mississippi drainage

Lake Kankakee Kankakee Outwash Plain Lake Wisconsin

Ohio drainage

Lake Monongahela Lake Tight Teays River

Hudson valley

Lake Albany Lake Passaic

New England

Lake Cape Cod Lake Connecticut Lake Hitchcock Lake Merrimack Lake Nantucket Sound Lake Stowe

California

Lake Cahuilla Lake Corcoran Lake Harper Lake Manix Lake Manly Lake Mojave Lake Russell Lake Tecopa Lake Thompson

New Mexico

Lake Palomas

Alaska

Lake Atna

South America

Lake Ballivián Cabana Lake Escara Inca Huasi Mataro Lake Minchin Ouki Sajsi Salinas Lake Tauca

Summary

List of prehi

.