Glaciation of North America has occurred many times in the past (Figure 2-1). Large ice sheets have advanced across this continent covering hundreds of thousands of square miles. The continental glacier that produced the landforms that we will be presented occurred during the Wisconsinan glaciation which ended approximately 10,000 years ago and was approximately 10,000 feet thick at its maximum. Ice sheets of this magnitude have the power to transport large quantities of sentiment long distances, and reshape entire landscapes during these glacial periods.
Glacial movement and deposition is a relatively simple process. As a glacier accumulates ice and snow, it begins to advance and move. To grow and survive, glaciers require low temperatures and consistent snowfall over a time period of thousands of years. The glaciers that affected Illinois originated in far-northern Canada. As the glacier advances, it scours the earth and pushes any material (rocks, trees etc.) out of its way. The material that the glacier moves around is carried along the base and sides of the glacier. The glaciers continue to advance until the leading edge of the glacier has high enough temperatures to cause melting, which is known as ablation. When ablation occurs faster than the accumulation of snowfall, the forward motion begins to stop and the margin of the glacier begins to retreat. As glaciers retreat, deposition produces a variety of new landforms.
Deposits associated with glaciation contain sediments and materials
consistent of the bedrock that the glacier crossed. Sediments from older
glaciers are also intertwined with deposits from bedrock. The deposits
from the most recent glacier, the Wisconsinan glacier, contain primarily
material from bedrock located in Northeastern Illinois, Wisconsin, Michigan
and Canada. Deposits left by the Wisconsinan glacier consist of sediments
that are economically valuable and are utilized for a variety of uses in
our society, such as building and road construction, glass manufacturing
and many other industries.