View source for Earth:Wisconsin glaciation

{{short description|North American glacial ice sheet}}
[[File:Iceage north-glacial hg.png|thumb|upright=1.4|Maximum glaciation of the northern hemisphere (black) during the Quaternary climatic cycles]]
The '''Wisconsin Glacial Episode''', also called the '''Wisconsin glaciation''', was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cordillera; the Innuitian ice sheet, which extended across the [[Place:Canadian Arctic Archipelago|Canadian Arctic Archipelago]]; the [[Earth:Greenland ice sheet|Greenland ice sheet]]; and the massive [[Earth:Laurentide Ice Sheet|Laurentide Ice Sheet]],<ref name="Harris1997" /> which covered the high latitudes of central and eastern North America. This advance was synchronous with global glaciation during the last glacial period, including the North American alpine glacier advance, known as the [[Earth:Pinedale glaciation|Pinedale glaciation]]. The Wisconsin glaciation extended from approximately 75,000 to 11,000 years ago, between the [[Earth:Sangamonian|Sangamonian Stage]] and the current interglacial, the [[Earth:Holocene|Holocene]]. The maximum ice extent occurred approximately 25,000–21,000 years ago during the last glacial maximum, also known as the ''Late Wisconsin'' in North America.

This glaciation radically altered the geography north of the Ohio River, including  in time the creation of the Great Lakes. At the height of the Wisconsin Episode glaciation, the [[Earth:Ice sheet|ice sheet]] covered most of {{wipe|Canada}}, the Upper Midwest, and New England, as well as parts of Idaho, Montana, and {{wipe|Washington (state)}}. On Kelleys Island in Lake Erie, northern New Jersey and in {{wipe|New York City}}'s Central Park,<ref>SERC Media; Glacial Grooves, Central Park; Image 14884 is a 208 by 173 pixel JPEG; Uploaded: Apr5 09; Wayne Powell, CUNY Brooklyn College; http://serc.carleton.edu/details/images/14884.html</ref> the [[Earth:Glacial striation|grooves left in rock]] by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, North America's northernmost point that remained south of the continental ice sheets. During much of the glaciation, sea level was low enough to permit land animals, including [[Humans|humans]], to occupy [[Earth:Beringia|Beringia]] (the Bering Land Bridge) and move between [[Earth:North America|North America]] and Siberia. As the glaciers retreated, glacial lakes were breached in great [[Earth:Glacial lake outburst flood|glacial lake outburst flood]]s such as the [[Earth:Kankakee Torrent|Kankakee Torrent]], which reshaped the landscape south of modern Chicago as far as the Ohio and Mississippi Rivers.

==Times==
Two related movements have been termed Wisconsin: Early Wisconsin and Late Wisconsin.<ref name=Sherzer>Chapter II. Glacial History of the Huron-Erie Basin; Geological Report on Wayne County; W.H. Sherzer; Michigan Geological and Biological Survey, Publication 12, Geological Series 9; Lansing, Michigan; Wynkoop Hallenbeck Crawford Co., State Printers; 1913</ref>{{rp|40–75}} The Early Wisconsin was the bigger of the two and extended farther west and south.  It retreated an unknown distance before halting.  During this period of quiet, the glacial deposits were eroded and weathered.  This first Wisconsin period erased all the [[Earth:Illinoian (stage)|Illinoian]] glacial topography that extended over.<ref name=Sherzer/> The Late Wisconsin ice sheet extended more towards the west than the earlier movements.  This may have been due to changes in the accumulation center of the ice sheet, topographic changes introduced by the Early phase or by pressure changes in the ice mass in the north.<ref name=Sherzer/> 
{|class="wikitable"
|-
! colspan="2" style=" background: #efefef;" | Table I
|-
! colspan="2" style="background: #ffdead;" | Table VII – Estimated Age of Glacial Episodes (Leverett) <ref name=Sherzer/>{{rp|74}} 
|- 
! Age
! Years before Present (YBP)
|-
| Culmination of Late Wisconsin
| align="right"| 50,000
|-
| Culmination of Early Wisconsin
| align="right"| 100,000
|-
| Beginning of Wisconsin
| align="right"| 150,000
|-
| Culmination of [[Earth:Illinoian (stage)|Illinoian]]
| align="right"| 300,000
|-
| Beginning of Illinoian
| align="right"| 350,000
|-
| Culmination of [[Earth:Pre-Illinoian|Pre-Illinoian]], i.e., old Nebraskan<ref name=Attig>Attig, John W.; Mickelson, David M. (1999). Glacial processes past and present. Boulder, Colo: The Geological Society of America, Inc. {{ISBN|0-8137-2337-X}}</ref><ref>Boellstorff, J (1978). "Chronology of some Late Cenozoic deposits from the central United States and the Ice Ages"(pdf). Transactions of the Nebraska Academy of Science 6: 35–49. Retrieved 2012-04-04.</ref>
| align="right"| 550,000
|-
| Beginning of Pre-Illinoian
| align="right"| 1,200,000
|}

==Continental ice sheets==

===Ice caps===
{| class="wikitable"
|-
! colspan="6" style=" background: #efefef;" | Table II
|-
! colspan="6" style="background: #ffdead;" | [[Earth:Ice cap|Ice Caps]]<ref name=Hill>Geological Framework and Glaciation of the Eastern Area; Christopher L. Hill; pg 82-98</ref>
|-
| Keewatin ice sheet
! [[Earth:Laurentide Ice Sheet|Laurentide Ice Sheet]]
| Nova Scotia Ice Cap
| Newfoundland Ice Cap
| [[Earth:Greenland ice sheet|Greenland Ice Cap]]
|}

===Labrador Ice Sheet===
The Labrador Ice Sheet centered east of Hudson Bay. Expanding towards the southwest, it reached into the eastern edge of Manitoba and across the Great Lakes to the Ohio River, upwards of {{convert|1600|mi|km}} from its source. Its eastern lobes covered New England and reached south to Cape Cod and Long Island, New York.<ref name=C&S3>Chamberlin, Thomas C. and Salisbury, Rollin T., Geology, 3 Vols. 1906, Vol III., pp. 330-333.</ref>

====Ice lobes====
{| class="wikitable"
|-
! colspan="6" style=" background: #efefef;" | Table III [[Earth:Laurentide Ice Sheet|Laurentide Ice Sheet]]
|-
! colspan="6" style="background: #ffdead;" | Glacial lobes and sublobes of the southern Laurentide Ice Sheet during the late Wisconsin Glaciation.<ref>The southern Laurentide Ice Sheet; Cavid M. Mickelson and Patrick M. Colgan; Department of Geology, University of Wisconsin Madison; Madison, Wisconsin; 2003</ref>
|- align="center"
! Major Lobes
| colspan="4" | Minor Lobes
|-
| Des Moines 
| Grantsburg
| St. Louis 
| Rainey
|
|-
| Lake Superior<ref name=Hill/>
| Wadena
| Chippewa<ref name=Hill/>
| Wisconsin Valley<ref name=Hill/>
| Langlade<ref name=Hill/>
|-
| Green Bay<ref name=Hill/>
|-
| rowspan="2"|Lake Michigan<ref name=Hill/>
| Delavan
| Harvard-Princeton
| Peoria
| Decatur
|-
| colspan="3"|Minor lobes: Milwaukee, Two Rivers; Straits of Mackinac
|
|-
| Saginaw
|-
| Lake Huron<ref name=Hill/>
| East White<ref name=Hill/>
| Miami<ref name=Hill/>
| Scioto<ref name=Hill/>
|
|-
| Lake Erie<ref name=Hill/>
|-
| Lake Ontario<ref name=Hill/>
| Lake Champlain<ref name=Hill/>
| Hudson River<ref name=Hill/>
|
|
|-
| unnamed lobe in Quebec – New England
| Connecticut Valley<ref name=Hill/>
| Buzzards Bay<ref name=Hill/>
| Cape Cod<ref name=Hill/>
| Georges Bank<ref name=Hill/>
|}

===Keewatin Ice Sheet===
The Keewatin Ice Sheet began west of Hudson Bay in the Canadian Territory of Keewatin. The ice moved south some {{convert|1500|mi|km}} into Kansas and Missouri.  To the west, it reached {{convert|1000|mi|km}} to the foothills of the Rocky Mountains.<ref name=C&S3/>

===Cordilleran Ice Sheet===
The Cordilleran Ice Sheet has left remnants throughout the Northern Rocky Mountains. Unlike the other two ice sheets, this one is mountain based covering British Columbia and reaching into northern {{wipe|Washington (state)}} State and Montana. The Cordilleran Ice Sheet has more of an Alpine style of many glaciers merged into a whole. The striations made by the ice field in moving over the bedrock show that it moved principally to the west through the passes of the coast range.<ref name=C&S3/>

==Formation of proglacial and prehistoric lakes==
[[File:Plate 53 - Glacial Lakes Duluth, Chicago, and Lundy (USGS 1915).JPG|thumb|upright=1.5|Proglacial lakes formed in the glacier carved Great Lakes basin, as the ice continued its long retreat]]
Whenever the ice sheet melted from the north at a [[Earth:Moraine|moraine]], water would begin to pond in the divide between a moraine and the ice front. The ice would act as a dam as water could not drain through the ice sheet, which in the Wisconsin period covered most of the proglacial river valleys. Numerous small, isolated water bodies formed between the moraine and the ice front.  As the ice sheet would continue to melt and recede northward, these ponds combined into [[Earth:Proglacial lake|proglacial lake]]s.  In areas without an available outlet, the water levels would either continue to rise until reaching one or more low spots along the rim of a moraine, or the ice sheet would retreat, opening access to a lower portion of the moraine.<ref name=Sherzer/>{{rp|40–99}} Multiple outlets could form through low spots too until one would become dominant after erosion lowered both the outlet and lake surface.

===Running  water===
Ice melt and rainfall carried large quantities of [[Earth:Clay|clay]], sand, and [[Earth:Gravel|gravel]] from the ice mass.  Clays could be moved long distances by moving water, while sand and gravel could not.  Thus, sand and gravel landforms developed along the sides and front of the ice sheet;<ref name=Sherzer/> elongated accumulations of this material are known as [[Earth:Kame|kame]]s.  Mounds along the frontal edge of the ice are called moraines.  Wherever a subglacial tunnel began infilling, long winding formations known as eskers would form. The sweeping plain of sand and gravel beyond the ice margin and a [[Earth:Terminal moraine|terminal moraine]] is called an [[Earth:Outwash plain|outwash plain]] .<ref name=Sherzer/> The materials left under the glacier when it melts back is called the ground moraine or [[Earth:Till plain|till plain]].<ref name=Sherzer/>  Till is highly permeable and creates a large ground reserve for water.  This formation is highly desirable for human economic development as a source of water.<ref name=Sherzer/>

==Stages of the Wisconsin episode==
{| class="wikitable"
|-
! colspan="4" style=" background: #efefef;" | Table IV
|-
! colspan="4" style="background: #ffdead;" | Maxima of the Wisconsin ice sheets<ref>Correlation of Wisconsin Glacial Maxima; Ernst Antevs; ca 1943; The Quaternary Geology of Southeastern Wisconsin with a Chapter on the Older Rock Formations, Professional Paper 106;  William C. Alden;  United States Geological Survey;  Government Printing Office, Washington, D.C.; 1918</ref>
|- align="center"
! Western Ice
! Eastern Ice
! Proximate years ago
! Position of ice border 
|-
| Mankato
| Valders
| align="center"|25,000
| Northern Washington, Idaho, and Montana to the Continental Divide – north of Edmonton – 65 miles east of Edmonton – northwest corner of North Dakota – Des Moines – west end of Lake Superior – Milwaukee – Port Huron – Buffalo – Schuylerville – St. Johnsbury.
|-
| rowspan="2" | (Great reduction of ice)
| Cary
| align="center"|27,500
|  Minneapolis – north Wisconsin – south of Chicago – Central Ohio – 50 miles south of Buffalo – Binghamton - Northampton
|-
| Tazewell<!-- column 1 occupied by (Great reduction of ice) -->
| align="center"|40,000
| Rockford, Ill. – Peoria – south of Indianapolis – north of Cincinnati – northwestern Pennsylvania – central Long Island
|-
| Iowan
| No known ice
| align="center"|65,500
| Northern Washington, Idaho, and Montana – northwest North Dakota – east central Iowa - Minneapolis
|}

==Role in human migration==
Prehistoric human migration was likely greatly influenced by this last glacial period, as during much of the Wisconsin era, the formation of a [[Earth:Land bridge|land bridge]] known as [[Earth:Beringia|Beringia]] across the Bering Strait is believed to have allowed human occupation of this area which provided potential access for some of the first humans to move between North America and Siberia in [[Earth:Asia|Asia]] (see Settlement of the Americas). Other human migration routes also opened during interglacial periods in both [[Earth:Europe|Europe]] and Asia.<ref name="Harm2005" />

==Flora and fauna==
North American flora and fauna species were distributed quite differently during the Wisconsin era, due to altered temperatures, surface water distribution, and in some cases coverage of earth surface by glaciers. A number of scientific studies have been conducted to determine species distribution, particularly during the Late Wisconsin and early to mid-Holocene. An example of findings is from the investigation of flora species using [[Biology:Pollen core|pollen core]] samples in present-day northern Arizona. Here in the Waterman Hills researchers found that ''[[Biology:Juniperus osteosperma|Juniperus osteosperma]]'' and ''[[Biology:Pinus monophylla|Pinus monophylla]]'' were early to mid-Holocene dominant trees, while ''[[Biology:Monardella arizonica|Monardella arizonica]]'' has been a continuously present understory plant. ''[[Biology:Celtis reticulata|Celtis reticulata]]'' is an example of a plant present in the early Holocene following Wisconsin glacial retreat, a species no longer present at the Waterman Mountains site.<ref name="Hogan2009" />

==See also==
<!-- alphabetical order please WP:SEEALSO -->
<!-- please add a short description WP:SEEALSO, via {{subst:AnnotatedListOfLinks}} or {{Annotated link}} -->
{{div col|colwidth=30em|small=yes}}
* {{Annotated link |Driftless Area}}
* {{Annotated link |Geology of Ontario}}
* {{Annotated link |Glacial history of Minnesota}}
* {{Annotated link |Glacial Lake Iroquois}}
* {{Annotated link |Ice Age Trail}}
* {{Annotated link |Ice core}}
* {{Annotated link |Last Glacial Period}}
* {{Annotated link |Retreat of glaciers since 1850}}
* {{Annotated link |Timeline of glaciation}}
* {{Annotated link |Younger Dryas}}
{{div col end}}
<!-- alphabetical order please WP:SEEALSO -->

=== Pleistocene historic names ===
{{div col}}
{| class="wikitable"
|+ Historical names of the "four major" glacials in four regions.
! Region
! Glacial 1
! Glacial 2
! Glacial 3
! Glacial 4
|-
| '''Alps'''
| [[Earth:Gunz glaciation|Günz]]
| [[Earth:Mindel glaciation|Mindel]]
| [[Earth:Riss glaciation|Riss]]
| [[Earth:Würm glaciation|Würm]]
|-
| '''North Europe'''
| [[Earth:Eburonian|Eburonian]]
| Elsterian
| Saalian
| Weichselian
|-
| '''British Isles'''
| [[Earth:Beestonian stage|Beestonian]]
| Anglian
| [[Earth:Wolstonian Stage|Wolstonian]]
| [[Earth:Devensian|Devensian]]
|-
| '''Midwest U.S.'''
| [[Earth:Pre-Illinoian|Nebraskan]]
| [[Earth:Kansan glaciation|Kansan]]
| [[Earth:Illinoian (stage)|Illinoian]]
| Wisconsinan
|}
{| class="wikitable"
|+ Historical names of interglacials.
! Region
! Interglacial 1
! Interglacial 2
! Interglacial 3
|-
| '''Alps'''
| [[Earth:Cromerian Stage|Günz-Mindel]]
| [[Earth:Hoxnian Stage|Mindel-Riss]]
| Riss-Würm
|-
| '''North Europe'''
| Waalian
| Holsteinian
| Eemian
|-
| '''British Isles'''
| [[Earth:Cromerian Stage|Cromerian]]
| [[Earth:Hoxnian Stage|Hoxnian]]
| Ipswichian
|-
| '''Midwest U.S.'''
| [[Earth:Pre-Illinoian|Aftonian]]
| Yarmouthian
| [[Earth:Sangamonian|Sangamonian]]
|}
{{div col end}}

==References==

{{Reflist|refs=
<ref name="Harm2005">Harm J. De Blij. 2005. ''Why geography matters: three challenges facing America'', 308 pages, p.69</ref>
<ref name="Harris1997">Ann G. Harris, Esther Tuttle, Sherwood D. Tuttle. 1997. ''Geology of National Parks: Fifth Edition'', Iowa, Kendall/Hunt Publishing {{ISBN|0-7872-5353-7}}</ref>
<ref name="Hogan2009">[http://www.globaltwitcher.com/artspec_information.asp?thingid=90792 C. Michael Hogan, 2009. ''Elephant Tree: Bursera microphylla'', GlobalTwitcher.com, ed. N. Stromberg]</ref>
}}

==External links and references==

* [https://www.britannica.com/science/Wisconsin-Glacial-Stage britannica.com reference]

{{Continental Glaciations}}

{{DEFAULTSORT:Wisconsin Glaciation}}
[[Category:Pleistocene geology]]

{{Sourceattribution|Wisconsin glaciation}}