The Laurentide ice sheet (LIS) was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glaciation epochs, from 2.58 million years ago to the present.

It was up to 2 mi (3.2 km) thick in Nunavik, Quebec, Canada, but much thinner at its edges, where nunataks were common in hilly areas.

That gave the Southwestern United States, otherwise a desert, abundant rainfall during ice ages, in extreme contrast to most other parts of the world which became exceedingly dry, though the effect of ice sheets in Europe had an analogous effect on the rainfall in Afghanistan, parts of Iran, possibly western Pakistan in winter, as well as North Africa.

That interrupted the thermohaline circulation, creating the brief Younger Dryas cold epoch and a temporary re-advance of the ice sheet,[6] which did not retreat from Nunavik until 6,500 years ago.

After the end of the Younger Dryas, the Laurentide Ice Sheet retreated rapidly to the north, becoming limited to only the Canadian Shield until even it became deglaciated.

[7] The ultimate collapse of the Laurentide Ice Sheet is also suspected to have influenced European agriculture indirectly through the rise of global sea levels.

The Cordilleran covered the region from the Pacific Ocean to the eastern front of the Rocky Mountains and the Labrador and Keewatin fields are referred to as the Laurentide Ice Sheet.

The Labrador covered spread over eastern Canada and the northeastern part of the United States abutting the Keewatin lobe in the western Great Lakes and Mississippi valley.

From the Escuminac center on the Magdalen Shelf, flowed onto the Acadian Peninsula of New Brunswick and southeastward, onto the Gaspe, burying the western end of Prince Edward Island and reached the head of Bay of Fundy.

Anchored in the mountain backbone of the west coast, the ice sheet dissipated north of the Alaska Range where the air was too dry to form glaciers.