thumb|upright=1.35|Maximum glaciation of the Northern Hemisphere (black) during the Quaternary climatic cycles

The Wisconsin glaciation, also called the Wisconsin glacial episode, was the most recent glacial period of the North American ice sheet complex, peaking more than 20,000 years ago. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cordillera; the Innuitian ice sheet, which extended across the Canadian Arctic Archipelago; the Greenland ice sheet; and the massive Laurentide Ice Sheet, the 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, to occupy Beringia (the Bering Land Bridge) and move between North America and Siberia. As the glaciers retreated, glacial lakes were breached in great glacial lake outburst floods such as the Kankakee Torrent, which reshaped the landscape south of modern Chicago as far as the Ohio and Mississippi Rivers.

Timeline

Two related movements have been termed Wisconsin: Early Wisconsin and Late Wisconsin. 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 Illinoian glacial topography that its glaciers extended over.

| align="right"| 550,000

|-

| Beginning of Pre-Illinoian

| align="right"| 1,200,000

|}

Continental ice sheets

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Ice caps

{| class="wikitable"

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! colspan="6" style=" background: #efefef;" | Table II

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! colspan="6" style="background: #ffdead;" | Ice Caps

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| Keewatin

! Laurentide Ice Sheet

| Nova Scotia Ice Cap

| Newfoundland Ice Cap

| Greenland Ice Cap

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Laurentide ice sheet

{| class="wikitable"

|-

! colspan="6" style=" background: #efefef;" | Table III Laurentide Ice Sheet

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! colspan="6" style="background: #ffdead;" | Glacial lobes and sublobes of the southern Laurentide Ice Sheet during the late Wisconsin Glaciation.

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! Major Lobes

| colspan="4" | Minor Lobes

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| Des Moines

| Grantsburg

| St. Louis

| Rainey

|

|-

| Lake Superior

| Wadena

| Chippewa

Keewatin

The Keewatin ice dome began west of Hudson Bay in the Canadian Territory of Keewatin. The ice moved south some into Kansas and Missouri. To the west, it reached to the foothills of the Rocky Mountains.

Innuitian ice sheet

The Innuitian ice sheet was centered on the Queen Elizabeth Islands.

Formation of proglacial and prehistoric lakes

thumb|right|upright=1.5|A diagram of the formation of the Great Lakes

Whenever the ice sheet melted from the north at a 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 proglacial lakes. 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. ]]Ice melt and rainfall carried large quantities of clay, sand, and 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;

|- align="center"

! Western Ice

! Eastern Ice

! Estimated years before present

! 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 land bridge known as 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 Asia (see Settlement of the Americas). Other human migration routes also opened during interglacial periods in both Europe and Asia.

  • Wisconsin Glacial Stage at the Encyclopædia Britannica