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Author: Admin | 2025-04-28
As featured in the November/December 2019 Gold Prospectors MagazineBy Tracy ReppGlaciation is a powerful earth process, characterized by the presence of huge volumes of land-based ice with the ability to completely rework and reshape landscapes. Over the last 3 billion years, there have been about 6 major periods of glaciation, periods that we call ice ages. The most recent ice age began about 34 million years ago (MYA). This ice age, characterized by periods of glacial advancement (i.e. glacial period) and glacial retreat (i.e. interglacial period) as all ice ages are, is considered by glaciologists to be ongoing because at least one permanent ice sheet, the Antarctic, remains. The latest phase of this ice age is called the Quaternary and it began roughly 2.5 MYA. Its last glacial period ended 11,700 years ago, beginning the interglacial period we live in today.During the most extreme of the Quaternary’s glacial periods, large ice sheets up to 2.5 miles thick formed at the more northern latitudes of North America, Siberia and Europe. The furthest and most recent advance of ice in North America, termed the Last Glacial Maximum (LGM), occurred about 26,500 years ago, and covered the areas shown in Figure 1, below.The massive ice sheets that form during glacial periods advance by “flowing” downhill and with their immense weight act like bulldozers, scraping over the surface of the earth. With thicknesses of up to 2.5 miles, the weight of this ice as it moves and picks up rock and debris, scours the landscape with incredible ease. Rocks called “erratics” up to 15,000 tons in size, which is about the size of the Brooklyn Bridge, can be plucked from the bedrock and carried hundreds of kilometers away from their source by the advancing ice. These rocks leave behind deep grooves in the bedrock
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