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Information about 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: The ice sheet covered up to two and a half million square kilometres at the Last Glacial Maximum and probably more than that in some previous periods such as the Kansan Glaciation, when it may have extended into the northeast extremity of Oregon and the Salmon River Mountains in Idaho. It is probable, though, that its northern margin was further south due to the influence of starvation caused by very low levels of precipitation.

At its eastern end the Cordilleran ice sheet merged with the Laurentide ice sheet at the Continental Divide, forming an area of ice that contained one and a half times as much water as the Antarctic ice sheet does today. At its western end it is believed nowadays that several small glacial refugia existed during the last glacial maximum below present sea level in now-submerged Hecate Strait and on the Brooks Peninsula in northern Vancouver Island. However, evidence of ice-free refugia above present sea level north of the Olympic Peninsula has been refuted by genetic and geological studies since the middle 1990s. The ice sheet faded north of the Alaska Range because the climate was too dry to form glaciers.

Unlike the Laurentide ice sheet, which is believed to have taken as much as eleven thousand years to fully melt, it is believed the Cordilleran ice sheet, except for areas that remain glaciated today, melted very quickly, probably in four thousand years or less. This rapid melting caused such floods as the overflow of Lake Missoula and shaped the topography of the extremely fertile Inland Empire of Eastern Washington.

Sea levels during glaciation

Because of the weight of the ice, the mainland of northwest North America was so depressed that sea levels at the Last Glacial Maximum were over a hundred metres higher than they are today (measured by the level of bedrock).

However, on the western edge at the Queen Charlotte Islands (which, contrary to "popular" myths of ice-free refugia, were entirely glaciated during the LGM) the lower thickness of the ice sheet meant that sea levels were as much as 170 metres lower than they are today, forming a large lake in the deepest parts of the strait. This was because the thickness of the centre of the ice sheet actually served to push upwards areas at the edge of the continental shelf which, even though glaciated, were displaced and lifted by the pressing of the crust further inland. The effect of this during deglaciation was that sea levels on the edge of the ice sheet, which naturally deglaciated first, initially rose due to an increase in the volume of water, but later fell due to rebound after deglaciation.

These effects are important because they have been used to explain how migrants to North America from Beringia were able to travel southward during the deglaciation process due purely to the exposure of submerged land between the mainland and numerous continental islands. They are also important for understanding the direction evolution has taken since the ice retreated.

Even today, the region is notable for its rapid changes in sea level, which, however, have little effect on most of the coast due to the numerous fjords.

See also

References

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Quaternary Period is the geologic time period from the end of the Pliocene Epoch roughly 1.806 million years ago to the present. The Quaternary includes 2 geologic subdivisions — the Pleistocene, including Gelasian that used to belong to Pliocene, and the Holocene
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North America is a continent [1] in the Earth's northern hemisphere and (chiefly) western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the south and west
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Spokane, Washington
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The Alaska Panhandle, sometimes referred to as Southeast Alaska, is the southeastern portion of the coast of the U.S. state of Alaska, which lies just west of the northern half of the Canadian province of British Columbia.
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Alaska Peninsula is a peninsula extending about 800 km (500 miles) to the southwest from the mainland of Alaska and ending in the Aleutian Islands. The peninsula separates the Pacific Ocean from Bristol Bay, an arm of the Bering Sea.
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continental shelf is the extended perimeter of each continent and associated coastal plain, which is covered during interglacial periods such as the current epoch by relatively shallow seas (known as shelf seas) and gulfs.
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In glaciology, starvation is said to occur when a glacier retreats not because of temperature increases, but due to precipitation being so low that ice flow downwards into the zone of ablation exceeds the replenishment from snowfall.
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Hecate Strait or Strait of Hecate (Haida: Seegaay) is a wide but shallow body of water parting the Queen Charlotte Islands from the mainland of British Columbia in Canada.
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Location British Columbia, Canada
Nearest city Port Alice
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The Olympic Peninsula is the large arm of land in western Washington state that lies across Puget Sound from Seattle. It is bounded on the west by the Pacific Ocean, the north by the Strait of Juan de Fuca, and the east by Puget Sound and the Hood Canal.
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Alaska Range



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glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water.
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flood is an overflow of an expanse of water that submerges land, a deluge.[1] In the sense of "flowing water", the word is applied to the inflow of the tide, as opposed to the outflow or "ebb".
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