The glacier valley where Glacier Valley Campground is located is an east-west valley created by the furthest reaches of the Green Bay lobe of the last glacier, part of the Laurentide Ice Sheet, some 20,000 years ago. The same glacier created lake Michigan.
For the past 2.5 million years the climate of the Northern Hemisphere has fluctuated between conditions of warm and cold. These cycles are the result of changes in the shape of the Earth’s orbit and the tilt of the Earth’s axis. The colder periods allowed the expansion of glaciers that covered large parts of the Northern Hemisphere.
Changes in climate have followed a regular pattern for the past 700,000 years. Each cycle lasted about 100,000 years and consisted of a long period of generally cooling climate during which glaciers grew, followed by shorter periods of conditions similar to or warmer than those of today.
Found now only in Antarctica and Greenland, ice sheets are enormous continental masses of glacial ice and snow expanding over 50,000 square kilometers (19,305 square miles). The ice sheet on Antarctica is over 4.7 kilometers (3 miles) thick in some areas.. Another example is the Greenland Ice Sheet. In the past ice ages, huge ice sheets also covered most of Canada (the Laurentide Ice Sheet).
The Laurentide Ice Sheet
About 100,000 years ago, the climate cooled again and a glacier, the Laurentide Ice Sheet, spread across the continent. Movement of the Laurentide Ice Sheet was shaped—to a certain extent—by the landscape. Highlands diverted the glacier into lobes (tongues or fingers of ice) that advanced into the lowland areas.
The Wisconsin Glaciation
The last cycle of climate cooling and glacier expansion in North America is known as the Wisconsin Glaciation. Near the end of the cycle, beginning about 26,000 years ago, the glacier began its advance into Wisconsin. It expanded for 10,000 years before temperatures warmed again and it began to melt back. It took another 6,500 years before the ice finally retreated from northern Wisconsin. (Click on the picture for a larger image.)
[singlepic id=53 w=180 h=240]The Laurentide Ice Sheet and the large volume of meltwater flowing from it greatly altered the landscape of Wisconsin. As a result, the landscape of the area glaciated during the last part of the Wisconsin Glaciation is notably different than that of areas glaciated earlier in the Ice Age (where erosion has destroyed most earlier glacial landforms) and areas that were never glaciated. For example, the outermost limit of the last glacier is marked by a conspicuous ridge of glacially deposited debris. The many lakes and wetlands and the irregular landscape that characterize so many areas of eastern and northern Wisconsin are also a direct result of the last glacier.
The Lake Michigan Lobe of the glacier flowed down the Lake Michigan lowland to central Indiana and Illinois. The Langlade, Wisconsin Valley, Chippewa, and Superior Lobes covered northern Wisconsin. The Green Bay Lobe flowed south in the Green Bay lowland, advancing over the east end of the Baraboo Hills and into both ends of Devils Lake gorge.
The edge of the Green Bay Lobe was probably a steep ice slope, perhaps several hundred feet high, littered with rock debris. Behind the steep slope, the ice surface probably rose very gently toward the center of the ice sheet, where the ice was thousands of feet thick.The flat area extending to the west and south of Lake Winnebago once was part of Glacial Lake Oshkosh, which filled a large part of the lowland as the Green Bay Lobe advanced and later melted away.
Glaciers and running water sculpt the land in different ways. While streams tend to cut winding curves and V-shaped valleys, glaciers carve nearly straight valleys with U-shaped cross-sections. The commonly V-shaped stream valley is converted to a U-shaped valley because the U-shape provides the least frictional resistance to the moving glacier. Because a glacier has a much greater viscosity and cross section than a river, its course has fewer and broader bends, and thus, the valley becomes straighter and smoother.
sources: Wikipedia, the Encyclopedia Britannica, and the Wisconsin Geological and Natural History Survey. Visit the WGNHS’s excellent website here.
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