Everything about Laurentide Ice Sheet totally explained
The
Laurentide Ice Sheet was a massive sheet of ice that covered hundreds of thousands of square miles, including most of
Canada and a large portion of the northern
United States, between c. 95,000 and c. 20,000 years before the present day. Its southern margin included the modern sites of
New York City and
Chicago, and then followed quite precisely the present course of the
Missouri River up to the northern slopes of the
Cypress Hills, beyond which it merged with the
Cordilleran Ice Sheet.
Up to two miles thick in
Nunavik but much thinner at its edges where
nunataks were common in hilly areas, this ice sheet was the primary feature of the
North American ice age.
Its cycles of growth and melting were a decisive influence on global
climate during its existence. This is because it served to divert the
jet stream which would otherwise flow from the relatively warm
Pacific Ocean through
Montana and
Minnesota to the south. This 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.
Its melting also caused major disruptions to the global climate cycle, because the huge influx of low-
salinity water into the
Atlantic Ocean initially via the
Susquehanna River and later via the
Saint Lawrence is believed to have disrupted the circulation of water from south to north in the Atlantic, creating the brief
Younger Dryas cold epoch and a brief re-advance of the ice sheet, which didn't retreat from Nunavik until 6,500 years ago.
Some people have argued that huge influxes of fresh water stopped the feeding of the ice sheet and
starved it, aiding the retreat that had already began. This is a controversial position because it's known that the North Atlantic was very cold throughout glacial periods and it's likely that the
anticyclone on top of the ice sheet helped sustain it through moist easterly winds which encouraged snow-bearing winds from the south.
During the
Kansan Glaciation the Laurentide Ice Sheet extended even further south, reaching as far as
Douglas County, Kansas and almost as far as
St. Louis, Missouri.
The ultimate collapse of the Laurentide Ice Sheet is also suspected in influencing European agriculture indirectly through the rise of global sea levels.
Canada's oldest ice is a remnant of the Laurentide Ice Sheet called the
Barnes Ice Cap on central
Baffin Island being 20,000 years old.
Further Information
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