<P> During the Würm, the Rhône Glacier covered the whole western Swiss plateau, reaching today's regions of Solothurn and Aarau . In the region of Bern it merged with the Aar glacier . The Rhine Glacier is currently the subject of the most detailed studies . Glaciers of the Reuss and the Limmat advanced sometimes as far as the Jura . Montane and piedmont glaciers formed the land by grinding away virtually all traces of the older Günz and Mindel glaciation, by depositing base moraines and terminal moraines of different retraction phases and loess deposits, and by the pro-glacial rivers' shifting and redepositing gravels . Beneath the surface, they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow . </P> <P> The Pinedale (central Rocky Mountains) or Fraser (Cordilleran Ice Sheet) glaciation was the last of the major glaciations to appear in the Rocky Mountains in the United States . The Pinedale lasted from approximately 30,000 to 10,000 years ago and was at its greatest extent between 23,500 and 21,000 years ago . This glaciation was somewhat distinct from the main Wisconsin glaciation as it was only loosely related to the giant ice sheets and was instead composed of mountain glaciers, merging into the Cordilleran Ice Sheet . The Cordilleran Ice Sheet produced features such as glacial Lake Missoula, which would break free from its ice dam causing the massive Missoula Floods . USGS geologists estimate that the cycle of flooding and reformation of the lake lasted an average of 55 years and that the floods occurred approximately 40 times over the 2,000 year period between 15,000 and 13,000 years ago . Glacial lake outburst floods such as these are not uncommon today in Iceland and other places . </P> <P> The Wisconsin Glacial Episode was the last major advance of continental glaciers in the North American Laurentide Ice Sheet . At the height of glaciation the Bering land bridge potentially permitted migration of mammals, including people, to North America from Siberia . </P> <P> It radically altered the geography of North America north of the Ohio River . At the height of the Wisconsin Episode glaciation, ice covered most of Canada, the Upper Midwest, and New England, as well as parts of Montana and Washington . On Kelleys Island in Lake Erie or in New York's Central Park, the grooves left by these glaciers can be easily observed . In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, which is the northernmost point in North America that remained south of the continental ice sheets . </P>

When did the glaciers melt in north america