Willmar Region - Robbins Island
In Minnesota, United States
Size:  (not chosen)
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A little tucked away corner in the Willmar park system. This marker talks about the recent glacial activity that formed the terrain and lakes nearby.
The last glacial period was the most recent glacial period within the current ice age, occurring in the Pleistocene epoch. It began about 110,000 years ago and ended between 10,000 and 15,000 BP. During this period there were several changes between glacier advance and retreat. The maximum extent of glaciation was approximately 18,000 years ago. While the general pattern of global cooling and glacier advance was similar, local differences in the development of glacier advance and retreat make it difficult to compare the details from continent to continent (see picture of ice core data below for differences).
The last glacial period is sometimes colloquially referred to as the last ice age, though this use is incorrect because an ice age is a longer period of cold temperature in which ice sheets cover large parts of the Earth. Glacials, on the other hand, refer to colder phases within an ice age that separate interglacials. Thus, the end of the last glacial period is not the end of the last ice age. The end of the last glacial period was about 12,500 years ago, while the end of the last ice age has not yet come: little evidence points to a stop of the glacial-interglacial cycle of the last million years.
The last glacial period is the best-known part of the current ice age, and has been intensively studied in North America, northern Eurasia, the Himalaya and other formerly glaciated regions around the world. The glaciations that occurred during this glacial period covered many areas, mainly on the Northern Hemisphere and - to a lesser extent - on the Southern Hemisphere. They have different names, historically developed and depending on their geographic distributions: Fraser (in the Pacific Cordillera of North America), Pinedale, Wisconsin (in central North America), Devensian (in the British Isles), Midlandian (in Ireland), Würm (in the Alps), Weichsel (or Vistula, in northern Central Europe), Valdai in Eastern Europe and Zyryanka in Siberia, Llanquihue in Chile and Otira in New Zealand.
The Wisconsin Glacial Episode was the last major advance of continental glaciers in the North American Laurentide ice sheet. This glaciation is made of three glacial maxima (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, perhaps as a byproduct of the Toba super eruption. Little is known about the Tenaya. The Tioga was the least severe and last of the Wisconsin Episode. It began about 30,000 years ago, reached its greatest advance 20,000 years ago, and ended about 10,000 years ago. At the height of glaciation the Bering land bridge permitted migration of mammals such as 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 Episode glaciation, ice covered most of Canada, the Upper Midwest, and New England, as well as parts of Montana and Washington. On Kelleys Island in Lake Erie or in New York's Central Park, the grooves 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 is the northernmost point in North America that remained south of the continental ice sheets.
The Great Lakes are the result of glacial scour and pooling of meltwater at the rim of the receding ice. 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.
With the assistance of several very large glacial lakes, it carved the gorge now known as the Upper Mississippi River, filling into the Driftless Area and probably creating an annual ice-dam-burst.
In its retreat, the Wisconsin Episode glaciation left terminal moraines that form Long Island, Nantucket and Cape Cod, and the Oak Ridges Moraine in south central Ontario, Canada. In Wisconsin itself, it left the Kettle Moraine. The drumlins and eskers formed at its melting edge are landmarks of the Lower Connecticut River Valley.
Nearby Robbins Island was created from the more recent Wisconsion Glacial Period.
For credit please send the answers to the following questions.
The drift was rich in what three minerals?
How many glaciers covered this area?
How long ago did the first glacier cross this area and which direction did it come from?
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Last Updated: on 09/26/2016 13:10:22 Pacific Daylight Time (20:10 GMT)
Coordinates are in the WGS84 datum