The Wisconsin Glaciation: North America's Last Great Ice Age

When Ice Sheets Covered Half the Continent

The most recent glacial period in North America, the Wisconsin Glaciation, began ~75,000 years ago and ended ~11,700 years ago (start of the Holocene). It was the last of the Pleistocene "ice ages."

Extent of the Ice

• Laurentide Ice Sheet: Covered all of Canada, the Great Lakes region, New England, and reached as far south as northern Ohio, Indiana, Illinois, Missouri, Nebraska, the Dakotas, Montana, Idaho, and Washington.
• Cordilleran Ice Sheet: Covered the Coast Mountains and Rockies of British Columbia, Alberta, and northern Washington/Idaho/Montana.
• Innuitian Ice Sheet: Covered the Canadian Arctic Archipelago.

At maximum (~20,000 years ago), ice volume lowered global sea level by ~120 meters (400 ft), exposing the Bering Land Bridge.

Causes

Driven by Milankovitch cycles—changes in Earth's orbit (eccentricity, obliquity, precession) that reduced summer insolation at high latitudes, allowing snow to persist and accumulate. Amplified by CO₂ feedback (lower greenhouse gases), albedo feedback (ice reflects sunlight), and possibly volcanic aerosols.

Legacy Landscapes

• Great Lakes: Carved by lobes of the Laurentide sheet.
• Finger Lakes, NY: Deepened river valleys.
• Moraines: Long Island, Cape Cod, Oak Ridges Moraine (Toronto), Kettle Moraine (WI).
• Drumlins, eskers, kames, outwash plains across the northern U.S. and Canada.
• Channeled Scablands (WA): Catastrophic floods from glacial Lake Missoula.

Human Context

Paleoindians entered via Beringia during the glaciation; the ice-free corridor opened ~14,000 years ago, and coastal migration routes existed earlier. The Younger Dryas cold snap (12,900–11,700 BP) briefly re-advanced ice before final retreat.