Editing Laurentide ice sheet

{{short description|Continental glacier in North America during the last ice age}}
{{Use dmy dates|date=April 2025}}
{{Infobox glacier
| child = 
| name = Laurentide ice sheet
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| photo =Laurentide ice sheet map.jpg
| photo_width =
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| photo_caption =The maximum extent of North American ice sheets during the [[Last Glacial Maximum]]
| map = <!-- or | map_image = -->
| map_width =
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| type = Continental
| location = [[North America]]
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| area = 
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| thickness =
| elevation_max = {{ubl|Foxe-Baffin Dome: {{convert|2200|to|2400|m|ft}} above sea level|Keewatin Dome:  {{convert|3200|m|ft}} above sea level<ref name=Lacelle2018>Lacelle, D.; Fisher, D. A.; Coulombe, S.; et al. (5 September 2018). "Buried remnants of the Laurentide Ice Sheet and connections to its surface elevation". ''Scientific Reports'' 8, 13286 (2018). {{doi|10.1038/s41598-018-31166-2}}.</ref>}}
| elevation_min = Sea level
| terminus = {{ubl|North – [[Arctic Ocean]]|East – [[Baffin Bay]]|South – 40 degrees north latitude|West – [[Rocky Mountains]]}}
| status =  Remnants: [[Barnes Ice Cap]], [[Penny Ice Cap]]<ref name=Lacelle2018/>
| embedded = 
}}

The '''Laurentide ice sheet''' (LIS) was a massive [[ice sheet|sheet of ice]] that covered millions of square miles, including most of [[Canada]] and a large portion of the [[Northern United States]], multiple times during the [[Quaternary glaciation]] epochs, from 2.58 million years ago to the present.<ref name="ICS StratChart 2022-02">{{cite web |title=Stratigraphic Chart 2022 |url=https://stratigraphy.org/ICSchart/ChronostratChart2022-02.pdf |publisher=International Stratigraphic Commission | date=February 2022  |access-date=4 June 2022}}</ref>

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]] ([[Minnesota]], [[Wisconsin]], and [[Michigan]]) to the [[Finger Lakes]], through [[Lake Champlain]] and [[Lake George (lake), New York|Lake George]] areas of [[New York (state)|New York]], across the northern [[Appalachians]] into and through all of [[New England]] and [[Nova Scotia]].

At times, the ice sheet's southern margin included the present-day sites of coastal towns of the [[Northeastern United States]], and cities such as [[Boston]] and [[New York City]] and Great Lakes coastal cities and towns as far south as [[Chicago]] and [[St. Louis, Missouri]], and then followed the present course of the [[Missouri River]] up to the northern slopes of the [[Cypress Hills (Canada)|Cypress Hills]], beyond which it merged with the [[Cordilleran Ice Sheet]]. The ice coverage extended approximately as far south as 38 degrees latitude mid-continent.<ref name="dyke_prest">{{cite journal |last1=Dyke |first1=A. S. |last2=Prest |first2=V. K. |year=1987|title=Late Wisconsinan and Holocene History of the Laurentide Ice Sheet|journal=Géographie Physique et Quaternaire |volume=41 |issue=2 |pages=237–263 |doi=10.7202/032681ar |doi-access=}}</ref>

==Description==
[[File:Retrait des glaces en Amérique.svg|thumb|Timeline of glacier retreat in North America]]
This ice sheet was the primary feature of the [[Pleistocene]] epoch in North America, commonly referred to as the [[Quaternary glaciation|ice age]]. During the [[Pre-Illinoian|Pre-Illinoian Stage]], the Laurentide Ice Sheet extended as far south as the [[Missouri River|Missouri]] and [[Ohio River]] valleys. It was up to {{convert|2|mi|km|abbr=on}} thick in [[Nunavik]], [[Quebec]], [[Canada]], but much thinner at its edges, where [[nunatak]]s were common in hilly areas. It created much of the surface geology of southern 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, [[Glacial Lake Iroquois|Lake Iroquois]] extended well beyond the boundaries of present-day [[Lake Ontario]], and drained down the Hudson River into the Atlantic Ocean.<ref>Flint, R.F. 1971. Glacial and Quaternary Geology. Wiley and Sons, NY. p. 892.</ref>

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]] southward, which would otherwise flow from the relatively warm [[Pacific Ocean]] through [[Montana]] and [[Minnesota]]. That 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]] had an analogous effect on the rainfall in [[Afghanistan]], parts of [[Iran]], possibly western [[Pakistan]] in winter, as well as [[North Africa]].
[[File:Sea Ice off Baffin Island.jpg|thumb|right|200px|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]]<ref name="Murton_Bateman">{{cite journal|last=Murton|first=J.B.|author2=Bateman, M.D. |author3=Dallimore, S.R |author4=Teller, J.T. |author5=Yang, Z. |year=2010|title=Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean|journal=Nature|volume=464|pages=740–743|doi=10.1038/nature08954|pmid=20360738|issue=7289|bibcode = 2010Natur.464..740M |s2cid=4425933}}</ref> is believed to have disrupted the formation of [[North Atlantic Deep Water]], the very saline, cold, deep water that flows from the [[Greenland Sea]]. That interrupted the [[thermohaline circulation]], creating the brief [[Younger Dryas]] cold epoch and a temporary re-advance of the ice sheet,<ref name="Broeckery_Denton">{{cite journal |last=Broecker |first=W.S. |author2=Denton, G.H. |year=1989 |title=The role of ocean-atmosphere reorganizations in glacial cycles |journal=Geochimica et Cosmochimica Acta |volume=53 |pages=2465–2501 |doi=10.1016/0016-7037(89)90123-3 |issue=10 |bibcode=1989GeCoA..53.2465B}}</ref> which did not retreat from [[Nunavik]] until 6,500 years ago.

After the end of the Younger Dryas, the Laurentide Ice Sheet retreated rapidly to the north, becoming limited to only the Canadian Shield until even it became deglaciated.<ref>{{cite journal |last1=Margold |first1=Marin |last2=Stokes |first2=Chris R. |last3=Clark |first3=Chris D. |date=1 June 2018 |title=Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet |journal=[[Quaternary Science Reviews]] |volume=189 |pages=1–30 |doi=10.1016/j.quascirev.2018.03.013 |bibcode=2018QSRv..189....1M |s2cid=53511921 |doi-access=free |url=https://durham-repository.worktribe.com/file/1333266/1/Accepted%20Journal%20Article }}</ref> The ultimate collapse of the Laurentide Ice Sheet is also suspected to have influenced European agriculture indirectly through the rise of global sea levels.

Canada's oldest ice is in remnants of the LIS: the [[Barnes Ice Cap]] and the [[Penny Ice Cap]].

==Ice centers==
<!-- ice centers, ice flows, ice domes -->
During the [[Late Pleistocene]], the Laurentide ice sheet reached from the [[Rocky Mountains]] eastward through the [[Great Lakes]], into [[New England]], covering nearly all of [[Canada]] east of the Rocky Mountains.<ref name=Hill2006>Geologic Framework and Glaciation of the Central Area, 1 January 2006; Christopher L. Hill; Boise State University, Boise, Idaho; 2006.</ref>
Three major ice centers formed in North America: the [[Labrador ice sheet|Labrador]], [[Keewatin ice sheet|Keewatin]], and [[Cordilleran Ice Sheet|Cordilleran]]. The Cordilleran covered the region from the Pacific Ocean to the eastern front of the Rocky Mountains and the 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 covered the western interior plains of North America from the [[Mackenzie River]] to the [[Missouri River]] and the upper reaches of the [[Mississippi River]]. The Labrador covered spread over [[eastern Canada]] and the northeastern part of the [[United States]] abutting the Keewatin lobe in the western [[Great Lakes]] and [[Mississippi River#Upper Mississippi|Mississippi valley]].<ref name=Hill2006/>

===Keewatin ice dome===
The Keewatin ice dome has had four or five primary lobes identified ice divides extending from a dome over west-central [[Kivalliq Region|Keewatin]] (Kivalliq). Two of the lobes abut the adjacent Labrador and Foxe-Baffin ice domes. The primary lobes flow (1) towards [[Manitoba]] and [[Saskatchewan]]; (2) toward [[Hudson Bay]]; (3) towards the [[Gulf of Boothia]], and (4) towards the [[Beaufort Sea]].<ref name=Dyke1987>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.</ref>

===Labrador ice dome===
[[File:Glacial lakes.jpg|thumb|right|Stages of [[proglacial lake]] development in the region of the current North American [[Great Lakes]]]]
The Labrador dome flowed across all of [[Maine]] and into the [[Gulf of St. Lawrence]], completely covering the [[The Maritimes|Maritime Provinces]]. The Appalachian Ice Complex, flowed from the [[Gaspé Peninsula]] over [[New Brunswick]], the [[Magdalen Islands|Magdalen Shelf]], and [[Nova Scotia]].<ref name=Dyke1987/>
The Labrador flow extended across the mouth of the [[St. Lawrence River]], reaching the [[Gaspé Peninsula]] and across [[Chaleur Bay]]. From the Escuminac center on the [[Magdalen Islands|Magdalen Shelf]], flowed onto the [[Acadian Peninsula]] of [[New Brunswick]] and southeastward, onto the Gaspe, burying the western end of [[Prince Edward Island]] and reached the head of [[Bay of Fundy]]. From the Gaspereau center, on the divide crossing New Brunswick flowed into the Bay of Fundy and Chaleur Bay.<ref name=Dyke1987/>

In New York, the ice that covered Manhattan was about 2,000 feet high before it began to melt in about 16,000 BC. The ice in the area disappeared around 10,000 BC. The ground in the New York area has since risen by more than 150&nbsp;ft because of the removal of the [[Post-glacial rebound|enormous weight of the melted ice]].<ref>{{cite news |last1=William J. Broad |title=How the Ice Age Shaped New York |url=https://www.nytimes.com/2018/06/05/science/how-the-ice-age-shaped-new-york.html |access-date=24 February 2019 |work=The New York Times |date=5 June 2018 |quote=the ice was about 2,000 feet thick over Manhattan}}</ref>

===Foxe-Baffin ice dome ===
The Foxe-Baffin ice dome 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]] and [[Southampton Island]]. Across southern Baffin Island, two divides created four additional lobes. The Penny Ice Divide split the [[Cumberland Peninsula]], where [[Pangnirtung]] created flow toward Home Bay on the north and Cumberland Sound on the south. The Amadjuak Ice Divide on the [[Hall Peninsula]], where [[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 Baffin Island are thought to be a remnant from this time period, but it was not a part of the Baffin ice flow, but an autonomous flow.<ref name=Dyke1987/>

==Adjacent ice sheets==
===Cordilleran ice sheet===
[[File:Peopling of America through Beringia.png|thumb|Approximate location of the [[Peopling of the Americas|ice-free corridor]] and specific [[Paleo-Indians|Paleoindian]] sites, according to the [[Clovis theory]]]]
The [[Cordilleran ice sheet]] covered up to {{convert|1500000|km2|mi2}} at the [[Last Glacial Maximum]].<ref>{{cite journal|title=Retreat pattern of the Cordilleran Ice Sheet in central British Columbia at the end of the last glaciation reconstructed from glacial meltwater landforms|journal=Boreas|volume=42|issue=4|pages=830–847|publisher=Wiley Online Library|date=18 February 2013|author1=Martin Margold|author2=Krister N. Jansson|author3=Johan Kleman|author4=Arjen P. Stroeven|author5=John J. Clague|doi=10.1111/bor.12007|bibcode=2013Borea..42..830M }}</ref> The eastern edge abutted the Laurentide ice sheet. The sheet was anchored in the [[Coast Mountains]] of [[British Columbia]] and [[Alberta]], south into the [[Cascade Range]] of [[Washington (state)|Washington]]. That 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]] where the air was too dry to form glaciers.<ref name=Hill2006/>
It is believed that the Cordilleran ice melted rapidly, in less than 4000 years. The water created numerous [[Proglacial lakes]] along the margins such as [[Lake Missoula]], often leading to catastrophic floods as with the [[Missoula Floods]]. Much of the topography of [[Eastern Washington]] and northern [[Montana]] and [[North Dakota]] was affected.<ref name=Hill2006/>

===Innuitian ice sheet===
The [[Innuitian ice sheet]], centered on the [[Queen Elizabeth Islands]], was connected to the northern part of the LIS.<ref name="a">{{cite journal|journal=[[Quaternary Science Reviews]]|volume=25|issue=7–8|pages=689–703|date=2005|title=The Innuitian Ice Sheet: configuration, dynamics and chronology|author1=J. England|author2=N. Atkinson|author3=J. Bednarski|author4=A.S. Dyke|author5=D.A. Hodgson|author6=C. Ó Cofaigh|doi=10.1016/j.quascirev.2005.08.007}}</ref>

==See also==
*[[Canadian Shield]]
*{{Annotated link|[[Laurentia]]}}
*[[Glacial history of Minnesota]]
*[[Driftless Area]]
*[[Lake Agassiz]]
*[[Wisconsin glaciation]]
*[[Innuitian ice sheet]]
*[[Cordilleran ice sheet]]

==References==
{{reflist}}

== Further reading ==
*{{cite journal |journal=University of Exeter |title=Noah's Flood Kick-started European Farming? |access-date=20 November 2007 |url=https://www.sciencedaily.com/releases/2007/11/071118213213.htm}}

== External links ==
* [http://www.museum.state.il.us/exhibits/ice_ages/laurentide_deglaciation.html The Retreat of Glaciers in North America] {{Webarchive|url=https://web.archive.org/web/20180226165117/http://www.museum.state.il.us/exhibits/ice_ages/laurentide_deglaciation.html |date=26 February 2018 }} (MPEG-Video)
{{Continental Glaciations}}
{{Pleistocene Lakes and Seas}}

{{DEFAULTSORT:Laurentide Ice Sheet}}
[[Category:Ice sheets]]
[[Category:Glaciology]]
[[Category:Glaciology of Canada]]
[[Category:Glaciology of the United States]]
[[Category:Geology of New York (state)]]
[[Category:Geology of Illinois]]
[[Category:Geology of Kansas]]
[[Category:Geology of Missouri]]
[[Category:Pleistocene]]
[[Category:Geological history of the Great Lakes]]
[[Category:Midwestern United States]]
[[Category:Northeastern United States]]