Wisconsin glaciation
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The Wisconsin (in North America), Weichsel (in Scandinavia), Devensian (in the British Isles) or Würm glaciation (in the Alps) is the most recent period of the Ice Age, and ended some 10,000 Before Present (BP). The Wisconsin/Weichsel/Devensian/Würm glaciation began about 70,000 BP, and reached its maximum extent about 18,000 BP. In Europe, the ice sheet reached northern Germany.
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The term ice age refers to all periods of glaciation during the Pleistocene, from 2.5 million years ago to 10,000 BP. In popular usage, 'the Ice Age' usually refers to this last cold phase, due to its shaping of some NorthernHemisphere landscapes and its influence on human prehistory.
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Weichsel glaciation, in Scandinavia
In Scandinavia, only the western parts of Jutland (a part of Denmark) were ice-free during the glaciation and a large part of what is today the North Sea was dry land connecting Jutland with Britain. It is also in Denmark that the only finds of Scandinavian ice-age animals older than 13,000 BP are found. In the period following the last interglacial period before the current one (Eemian interglacial era) the coast of Norway was also ice-free.
The Baltic Sea, with its unique brackish water, is a result of meltwater from the Weichsel glaciation combining with saltwater from the North Sea when the straits between Sweden and Denmark opened about 7,000 BP.
Overlaying ice had exerted pressure on the earth's surface. As a result of melting ice, the land has continued to rise yearly in Scandinavia, mostly in northern Sweden and Finland where the land is rising at a rate of as much as 8-9 mm per year, or 1 meters in 100 years. This important for archeologists since a village that was coastal in the Stone Age now is inland.
Devensian glaciation
The name Devensian glaciation is used by British geologists and archaeologists and refers to what is often popularly meant by the latest Ice Age.
It was the final glacial phase of the Pleistocene and its deposits have been found overlying material from the preceding Ipswichian interglacial and lying beneath those from the following Flandrian stage of the Holocene.
The latter part of the Devensian includes Pollen zones I-IV, the Allerød and Bølling Oscillations and the Dryas climatic stages.
Wisconsin glaciation, in North America
The Wisconsin or Wisconsinian was the last major advance of continental glaciers in North America. This glaciation is made of three glacial maximums (commonly called ice ages) separated by interglacial periods (such as the one we are living in). These ice ages are called (from oldest to youngest); Tahoe, Tenaya and Tioga. The Tahoe reached its maximum extent perhaps about 70,000 years ago while little is known about the Tenaya. The Tioga was the least severe and last of the Wisconsinan group and reached its greatest advance 20,000 years ago and ended about 10,000 years before present (it started 30,000 years ago). At the height of glaciation the Bering land bridge permitted migration of mammals and humans to North America from Siberia.
It radically altered the geography of North America north of the Ohio River. At the height of the Wisconsin glaciation, ice covered most of Canada, the Upper Midwest, and New England, as well as parts of Montana and Washington. On Kelly's Island in Lake Erie or in New York's Central Park, the scour marks left 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, which are the northernmost point in North America that remained south of the continental ice sheets.
The Great Lakes are the result of pooling of glacial meltwater at the rim of the receding glaciers. When the enormous mass of the continental ice sheet retreated, the Great Lakes began gradually moving south due to isostatic rebound of the north shore. Niagara Falls is also a product of the glaciation, as is the course of the Ohio River, which largely supplanted the prior Teays River.
In its retreat, the Wisconsin glaciation left terminal moraines that form Long Island, Nantucket and Cape Cod, and the Oak Ridges Moraine in south central Ontario, Canada. The drumlins and eskers formed at its melting edge are landmarks of the Lower Connecticut River Valley.
See also
References
- Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7
- E. C. Pielou 1991. After the Ice Age : The Return of Life to Glaciated North America (University Of Chicago Press) ISBN 0226668126 (paperback 1992)da:Weichsel-istiden
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