Wisconsin glaciation

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Maximum glaciation of the Northern Hemisphere (black) during the Quaternary climatic cycles Iceage north-glacial hg.png
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 Canadian Arctic Archipelago; the Greenland ice sheet; and the massive Laurentide Ice Sheet, [1] 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 Pinedale glaciation. The Wisconsin glaciation extended from approximately 75,000 to 11,000 years ago, between the Sangamonian Stage and the current interglacial, the 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.

Contents

The Last Glacial Period caused a much lower global sea level Global sea levels during the last Ice Age.jpg
The Last Glacial Period caused a much lower global sea level

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 ice sheet covered most of Canada, the Upper Midwest, and New England, as well as parts of Idaho, Montana, and Washington. On Kelleys Island in Lake Erie, northern New Jersey and in New York City's Central Park, [2] 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.

Times

Two related movements have been termed Wisconsin: Early Wisconsin and Late Wisconsin. [3] :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 Illinoian glacial topography that its glaciers extended over. [3] 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. [3]

Table I
Table VII – Estimated Age of Glacial Episodes (Leverett) [3] :74
AgeYears before Present (YBP)
Culmination of Late Wisconsin50,000
Culmination of Early Wisconsin100,000
Beginning of Wisconsin150,000
Culmination of Illinoian 300,000
Beginning of Illinoian350,000
Culmination of Pre-Illinoian, i.e., old Nebraskan [4] [5] 550,000
Beginning of Pre-Illinoian1,200,000

Continental ice sheets

Ice caps

Table II
Ice Caps [6]
Keewatin ice sheet Laurentide Ice Sheet Nova Scotia Ice CapNewfoundland Ice Cap 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 1,600 miles (2,600 km) from its source. Its eastern lobes covered New England and reached south to Cape Cod and Long Island, New York. [7]

Ice lobes

Table III Laurentide Ice Sheet
Glacial lobes and sublobes of the southern Laurentide Ice Sheet during the late Wisconsin Glaciation. [8]
Major LobesMinor Lobes
Des MoinesGrantsburgSt. LouisRainey
Lake Superior [6] WadenaChippewa [6] Wisconsin Valley [6] Langlade [6]
Green Bay [6]
Lake Michigan [6] DelavanHarvard-PrincetonPeoriaDecatur
Minor lobes: Milwaukee, Two Rivers; Straits of Mackinac
Saginaw
Lake Huron [6] East White [6] Miami [6] Scioto [6]
Lake Erie [6]
Lake Ontario [6] Lake Champlain [6] Hudson River [6]
unnamed lobe in Quebec – New EnglandConnecticut Valley [6] Buzzards Bay [6] Cape Cod [6] Georges Bank [6]

Keewatin Ice Sheet

The Keewatin Ice Sheet began west of Hudson Bay in the Canadian Territory of Keewatin. The ice moved south some 1,500 miles (2,400 km) into Kansas and Missouri. To the west, it reached 1,000 miles (1,600 km) to the foothills of the Rocky Mountains. [7]

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 Washington 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. [7]

Formation of proglacial and prehistoric lakes

Proglacial lakes formed in the glacier carved Great Lakes basin, as the ice continued its long retreat Plate 53 - Glacial Lakes Duluth, Chicago, and Lundy (USGS 1915).JPG
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 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. [3] :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 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; [3] elongated accumulations of this material are known as kames. 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 terminal moraine is called an outwash plain . [3] The materials left under the glacier when it melts back is called the ground moraine or till plain. [3] 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. [3]

Stages of the Wisconsin episode

Table IV
Maxima of the Wisconsin ice sheets [9]
Western IceEastern IceProximate years agoPosition of ice border
MankatoValders25,000Northern 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.
(Great reduction of ice)Cary27,500Minneapolis – north Wisconsin – south of Chicago – Central Ohio – 50 miles south of Buffalo – Binghamton - Northampton
Tazewell40,000Rockford, Ill. – Peoria – south of Indianapolis – north of Cincinnati – northwestern Pennsylvania – central Long Island
IowanNo known ice65,500Northern 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. [10]

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 pollen core samples in present-day northern Arizona. Here in the Waterman Hills researchers found that Juniperus osteosperma and Pinus monophylla were early to mid-Holocene dominant trees, while Monardella arizonica has been a continuously present understory plant. 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. [11]

See also

Pleistocene historic names

Historical names of the "four major" glacials in four regions.
RegionGlacial 1Glacial 2Glacial 3Glacial 4
Alps Günz Mindel Riss Würm
North Europe Eburonian Elsterian Saalian Weichselian
British Isles Beestonian Anglian Wolstonian Devensian
Midwest U.S. Nebraskan Kansan Illinoian Wisconsinan
Historical names of interglacials.
RegionInterglacial 1Interglacial 2Interglacial 3
Alps Günz-Mindel Mindel-Riss Riss-Würm
North EuropeWaalianHolsteinian Eemian
British Isles Cromerian Hoxnian Ipswichian
Midwest U.S. Aftonian Yarmouthian Sangamonian

Related Research Articles

<span class="mw-page-title-main">Moraine</span> Glacially formed accumulation of debris

A moraine is any accumulation of unconsolidated debris, sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice sheet. It may consist of partly rounded particles ranging in size from boulders down to gravel and sand, in a groundmass of finely-divided clayey material sometimes called glacial flour. Lateral moraines are those formed at the side of the ice flow, and terminal moraines were formed at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines and medial moraines.

<span class="mw-page-title-main">Glaciology</span> Scientific study of ice and natural phenomena involving ice

Glaciology is the scientific study of glaciers, or, more generally, ice and natural phenomena that involve ice.

A kame delta is a glacial landform formed by a stream of melt water flowing through or around a glacier and depositing material, known as kame deposits. Upon entering a proglacial lake at the end (terminus) of a glacier, the river/stream deposit these sediments. This landform can be observed after the glacier has melted and the delta's asymmetrical triangular shape is visible. Once the glacier melts, the edges of the delta may subside as ice under it melts. Glacial till is deposited on the lateral sides of the delta, as the glacier melts.

<span class="mw-page-title-main">Last Glacial Period</span> Period of major glaciations of the Northern Hemisphere (115,000–12,000 years ago)

The Last Glacial Period (LGP), also known colloquially as the Last Ice Age or simply Ice Age, occurred from the end of the Last Interglacial to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago.

<span class="mw-page-title-main">Proglacial lake</span> Lake formed by the action of ice

In geology, a proglacial lake is a lake formed either by the damming action of a moraine during the retreat of a melting glacier, a glacial ice dam, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around the ice. At the end of the last ice age about 10,000 years ago, large proglacial lakes were a widespread feature in the northern hemisphere.

<span class="mw-page-title-main">Laurentide Ice Sheet</span> Continental glacier in North America during the last ice age

The Laurentide Ice Sheet was a massive 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 glacial epochs, from 2.58 million years ago to the present.

<span class="mw-page-title-main">Till plain</span> Plain of glacial till

Till plains are an extensive flat plain of glacial till that forms when a sheet of ice becomes detached from the main body of a glacier and melts in place, depositing the sediments it carried. Ground moraines are formed with melts out of the glacier in irregular heaps, forming rolling hills. Till plains are common in areas such as the Midwestern United States, due to multiple glaciation events that occurred in the Holocene epoch. During this period, the Laurentide Ice Sheet advanced and retreated during the Pleistocene epoch. Till plains formed by the Wisconsin glaciation cover much of the Midwest, including North Dakota, South Dakota, Indiana, Minnesota, Wisconsin, Iowa, Illinois, and northern Ohio.

<span class="mw-page-title-main">Cordilleran ice sheet</span> Major ice sheet that periodically covered large parts of North America during glacial periods

The Cordilleran ice sheet was a major ice sheet that periodically covered large parts of North America during glacial periods over the last ~2.6 million years.

<span class="mw-page-title-main">Glacial history of Minnesota</span>

The glacial history of Minnesota is most defined since the onset of the last glacial period, which ended some 10,000 years ago. Within the last million years, most of the Midwestern United States and much of Canada were covered at one time or another with an ice sheet. This continental glacier had a profound effect on the surface features of the area over which it moved. Vast quantities of rock and soil were scraped from the glacial centers to its margins by slowly moving ice and redeposited as drift or till. Much of this drift was dumped into old preglacial river valleys, while some of it was heaped into belts of hills at the margin of the glacier. The chief result of glaciation has been the modification of the preglacial topography by the deposition of drift over the countryside. However, continental glaciers possess great power of erosion and may actually modify the preglacial land surface by scouring and abrading rather than by the deposition of the drift.

Fluvioglacial landforms or glaciofluvial landforms are those that result from the associated erosion and deposition of sediments caused by glacial meltwater. Glaciers contain suspended sediment loads, much of which is initially picked up from the underlying landmass. Landforms are shaped by glacial erosion through processes such as glacial quarrying, abrasion, and meltwater. Glacial meltwater contributes to the erosion of bedrock through both mechanical and chemical processes. Fluvio-glacial processes can occur on the surface and within the glacier. The deposits that happen within the glacier are revealed after the entire glacier melts or partially retreats. Fluvio-glacial landforms and erosional surfaces include: outwash plains, kames, kame terraces, kettle holes, eskers, varves, and proglacial lakes.

<span class="mw-page-title-main">Proglacial lakes of Minnesota</span>

The proglacial lakes of Minnesota were lakes created in what is now the U.S. state of Minnesota in central North America in the waning years of the last glacial period. As the Laurentide Ice Sheet decayed at the end of the Wisconsin glaciation, lakes were created in depressions or behind moraines left by the glaciers. Evidence for these lakes is provided by low relief topography and glaciolacustrine sedimentary deposits. Not all contemporaneous, these glacial lakes drained after the retreat of the lobes of the ice sheets that blocked their outlets, or whose meltwaters fed them. There were a number of large lakes, one of which, Glacial Lake Agassiz, was the largest body of freshwater known to have existed on the North American continent; there were also dozens of smaller and more transitory lakes filled from glacial meltwater, which shrank or dried as the ice sheet retreated north.

Lake Bassano was a proglacial lake that formed in the Late Pleistocene during the deglaciation of south-central Alberta by the impoundment of a re-established drainage system and addition of glacial meltwater. It is associated with the development of through-flowing drainage within the Red Deer River basin in particular, and the South Saskatchewan drainage network in general. Approximately 7,500 square kilometres (2,900 sq mi) of the Bassano basin is covered with lacustrine sediments. These sediments are bordered by the topographically higher Buffalo Lake Moraine to the west, the Suffield Moraine to the east and the Lethbridge Moraine to the south.

<span class="mw-page-title-main">Geology of New England</span> Overview of the geology of New England

New England is a region in the North Eastern United States consisting of the states Rhode Island, Connecticut, Massachusetts, New Hampshire, Vermont, and Maine. Most of New England consists geologically of volcanic island arcs that accreted onto the eastern edge of the Laurentian Craton in prehistoric times. Much of the bedrock found in New England is heavily metamorphosed due to the numerous mountain building events that occurred in the region. These events culminated in the formation of Pangaea; the coastline as it exists today was created by rifting during the Jurassic and Cretaceous periods. The most recent rock layers are glacial conglomerates.

<span class="mw-page-title-main">Kankakee Torrent</span>

The Kankakee Torrent was a catastrophic flood that occurred about 19,000 calibrated years ago in the Midwestern United States. It resulted from a breach of moraines forming a large glacial lake fed by the melting of the Late Wisconsin Laurentide Ice Sheet. The point of origin of the flood was Lake Chicago. The landscape south of Chicago still shows the effects of the torrent, particularly at Kankakee River State Park and on the Illinois River at Starved Rock State Park.

Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice sheet or frozen surface layer, and the resulting exposure of the Earth's surface. The decline of the cryosphere due to ablation can occur on any scale from global to localized to a particular glacier. After the Last Glacial Maximum, the last deglaciation begun, which lasted until the early Holocene. Around much of Earth, deglaciation during the last 100 years has been accelerating as a result of climate change, partly brought on by anthropogenic changes to greenhouse gases.

<span class="mw-page-title-main">Lake Kankakee</span>

Lake Kankakee formed 14,000 years before present (YBP) in the valley of the Kankakee River. It developed from the outwash of the Michigan Lobe, Saginaw Lobe, and the Huron-Erie Lobe of the Wisconsin glaciation. These three ice sheets formed a basin across Northwestern Indiana. It was a time when the glaciers were receding, but had stopped for a thousand years in these locations. The lake drained about 13,000 YBP, until reaching the level of the Momence Ledge. The outcropping of limestone created an artificial base level, holding water throughout the upper basin, creating the Grand Kankakee Marsh.

<span class="mw-page-title-main">Vashon Glaciation</span>

The Vashon Glaciation, Vashon Stadial or Vashon Stade is a local term for the most recent period of very cold climate in which during its peak, glaciers covered the entire Salish Sea as well as present day Seattle, Tacoma, Olympia and other surrounding areas in the western part of present-day Washington (state) of the United States of America. This occurred during a cold period around the world known as the last glacial period. This was the most recent cold period of the Quaternary glaciation, the time period in which the arctic ice sheets have existed. The Quaternary Glaciation is part of the Late Cenozoic Ice Age, which began 33.9 million years ago and is ongoing. It is the time period in which the Antarctic ice cap has existed.

<span class="mw-page-title-main">Lake Jordan (Montana)</span> Glacial lake (former) in Montana along the Jordan River , .

Lake Jordan was a glacial lake formed during the late Pleistocene along the Jordan River. After the Laurentide Ice Sheet retreated, water melting off the glacier accumulated between the Rocky Mountains and the ice sheet. The lake drained along the front of the ice sheet, eastward towards the Yellowstone River and Glacial Lake Glendive.

<span class="mw-page-title-main">Lake Cut Bank</span> Glacial lake (former) in Glacier, Montana along the Cut Bank Creek.

Lake Cut Bank was a glacial lake formed during the late Pleistocene along the Missouri and Sun Rivers. After the Laurentide Ice Sheet retreated, water melting off the glacier accumulated between the Rocky Mountinas and the ice sheet. The lake drained along the front of the ice sheet, eastward towards the Judith River and the Missouri River.

<span class="mw-page-title-main">Lake Chouteau</span> Glacial lake (former) in Teton, Montana

Lake Chouteau was a glacial lake formed during the late Pleistocene along the Teton River. After the Laurentide Ice Sheet retreated, water melting off the glacier accumulated between the Rocky Mountains and the ice sheet. The lake drained along the front of the ice sheet, eastward towards the Judith River and the Missouri River.

References

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  11. C. Michael Hogan, 2009. Elephant Tree: Bursera microphylla, GlobalTwitcher.com, ed. N. Stromberg