Laurentide ice sheet

Laurentide ice sheet

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 did not 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 is known that the North Atlantic was very cold throughout glacial periods and it is 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 Pre-Illinoian Stage 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.

ee also

*Canadian Shield
*Glacial history of Minnesota
*Lake Agassiz
*Wisconsin glaciation

References

*cite journal |journal=University of Exeter |title=Noah's Flood Kick-started European Farming? |accessdate=2007-11-20 |url=http://www.sciencedaily.com­/releases/2007/11/071118213213.htm

External links

* [http://www.museum.state.il.us/exhibits/ice_ages/laurentide_deglaciation.html The Retreat of Glaciers in North America] (MPEG-Video)


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • Laurentide Ice Sheet — Principal glacial cover of North America during the Pleistocene epoch (1.8 million–10,000 years ago). At its maximum extent it spread as far south as latitude 37° N and covered an area of more than 5 million sq mi (13 million sq km). In some… …   Universalium

  • Ice sheet dynamics — describe the motion within large bodies of ice, such those currently on Greenland and Antarctica. Ice motion is dominated by the movement of glaciers, whose gravity driven activity is controlled by two main variable factors: the temperature and… …   Wikipedia

  • Ice sheet — An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² (20,000 mile²). [cite web|url=http://gemini.oscs.montana.edu/ geol445/hyperglac/glossary.htm|accessdate=2006 08 22|title=Glossary of Important… …   Wikipedia

  • Cordilleran Ice Sheet — The Cordilleran ice sheet was a major ice sheet that covered, during glacial periods of the Quaternary, a large area of North America. This included the following areas: Western Montana The Idaho Panhandle Northern Washington state down to about… …   Wikipedia

  • Patagonian Ice Sheet — The Patagonian Ice Sheet was a large elongated and narrow ice sheet that covered all of Chile south of approximately present day Puerto Montt during the Llanquihue glaciation. Some maps have the Patagonian Ice Sheet connected to the icecaps of… …   Wikipedia

  • ice — iceless, adj. icelike, adj. /uys/, n., v., iced, icing, adj. n. 1. the solid form of water, produced by freezing; frozen water. 2. the frozen surface of a body of water. 3. any substance resembling frozen water: camphor ice …   Universalium

  • Little Ice Age — The reconstructed depth of the Little Ice Age varies between different studies (anomalies shown are from the 1950–80 reference period). The Little Ice Age (LIA) was a period of cooling that occurred after the Medieval Warm Period (Medieval… …   Wikipedia

  • Barnes Ice Cap — The Barnes Ice Cap is an ice cap located in central Baffin Island, Nunavut, Canada. It covers close to 6,000 km2 and has been thinning due to global warming. [http://www.hfxnews.ca/index.cfm?sid=96564 sc=89 Halifax, The Daily News: Local News |… …   Wikipedia

  • Pleistocene Epoch — Earlier and longer of the two epochs that constitute the Quaternary Period. The Pleistocene began с 1.8 million years ago and ended с 10,000 years ago. It was preceded by the Pliocene Epoch of the Tertiary Period and followed by the Holocene… …   Universalium

  • Heinrich event — Heinrich events, first described by marine geologist Hartmut Heinrich, occurred during the last glacial period, or ice age . During such events, armadas of icebergs broke off from glaciers and traversed the North Atlantic. The icebergs contained… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”