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Unlike the Laurentide Ice Sheet, which may have taken as many as eleven thousand years to fully melt, [3] the Cordilleran ice sheet melted very quickly, probably in four thousand years or less. [4] This rapid melting caused floods such as the overflow of Lake Missoula and shaped the topography of the fertile Inland Empire of Eastern Washington. [5]
The Cordilleran ice sheet dammed up Glacial Lake Missoula at the Purcell Trench Lobe. [10] A series of floods occurring over the period of 18,000 to 13,000 years ago swept over the landscape when the ice dam broke. The eroded channels also show an anastomosing, or braided, appearance.
Running water has etched out the grain of the range, landslides have softened the abrupt edges, homegrown glaciers have scoured the peaks and high valleys and, during the Ice Age, the Cordilleran Ice Sheet overrode almost all the range and rearranged courses of streams. Erosion has written and still writes its own history in the mountains, but ...
Drumlins occur in various shapes and sizes, [6] including symmetrical (about the long axis), spindle, parabolic forms, and transverse asymmetrical forms. Generally, they are elongated, oval-shaped hills, with a long axis parallel to the orientation of ice flow and with an up-ice (stoss) face that is generally steeper than the down-ice (lee) face.
The Cordilleran Ice Sheet has left remnants throughout the Northern Rocky Mountains, covering British Columbia and reaching into northern Washington State and Montana. The Cordilleran ice sheet has more of an Alpine style of many glaciers merged into a whole.
The Okanogan lobe of the Cordilleran Ice Sheet moved down the Okanogan River valley, covering 500 mi 2 of the Waterville Plateau and blocked the ancient route of the Columbia River, backing up water to create Glacial Lake Columbia.
The Cordilleran ice sheet covered up to 1,500,000 square kilometres (580,000 sq mi) at the Last Glacial Maximum. [11] The eastern edge abutted the Laurentide ice sheet. The sheet was anchored in the Coast Mountains of British Columbia and Alberta, south into the Cascade Range of Washington. That is one and a half times the water held in the ...
The Laurentide and Cordilleran ice sheets overtook the majority of Canada and parts of the United States during the last glaciation. South of the glaciers, the major biomes on the continent were tropical semi-desert, subalpine parkland, temperate steppe grassland, and main taiga . [ 7 ]