Glaciation

A glacier can be defined as a large, slowly moving mass of ice and compact snow. Today glaciers are found only in the polar regions and in high mountainous areas, but in the past, they covered vast areas of the Earth’s surface, and shaped much of the landscape that we see today.

During the Pleistocene Epoch (a geologic time period from 1.8 million years ago to about 10,000 years ago), cycles of glaciation expansion and retreat occurred repeatedly. Glacial cycles are composed of both glacial periods, in which the climate cools and glaciers grow, and interglacial periods, in which a warming climate causes the ice bodies to recede.

The last glacial period in North America is called the Wisconsinan Glaciation. It is divided into Early (80,000 – 55,000 years ago), and Late (25,000 – 10,000 years ago) glacial stages, with an intervening interglacial stage (55,000 - 25,000 years ago).
During the Late Wisconsinan glacial stage, most of Canada and parts of the northern United States were covered by two massive ice sheets: the Cordilleran which lay to the west of the Rocky Mountains and the Laurentide to the east. (An ice sheet is formed through the convergence of several glaciers and is the largest of all ice bodies.) These ice sheets are estimated to have had a maximum thickness of between 2– 4 kilometers and as a result would have posed an impassable barrier to people and animals.

Global glaciation simulation

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