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Glacial and Periglacial Geomorphology

Glacial and Periglacial Geomorphology - Glacial 1 Glacial...

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Glacial: 1 Glacial and Periglacial Geomorphology Ice Ages Glacier Mass Balance Glacial Geomorphology Erosion Transport and Deposition Landforms of Continental Glaciation Periglacial geomorphology A glacier is an accumulation of ice affected by past or present movement. In other words, a lump of ice is not a glacier unless it has moved. Glaciers form when the amount of snow accumulating in the winter is greater than the ablation of the snow (melting and sublimation) in the summer. If this continues for a period of years, the snow can become ice and flow under the force of gravity. Glaciers are presently found in Antarctica and Greenland–these are continental glaciers –and in mountainous areas where the conditions are right– alpine glaciers . Ice Ages There have been cold periods over much of earth history. We will look at the most recent ones. For a long time we thought that there were four major advances of glaciers in the last 1 million years. But now we have found ways to measure past temperatures (using such evidence as forms of oxygen stored in glaciers) and it seams that in the last two to three million years, there have been roughly 18 cold spells with warm spells in between. (The time of ice ages and the number is not known precisely. Don ± t worry if you see different numbers in the text or elsewhere.) It is likely that we are in one of the warm spells now and that another cold period will arrive sometime in the future (but don't lose sleep over it, it will be a while). During cold periods, glaciers advance and they retreat during warm periods. The last major glacial advance began about 28,000 years ago and reached its peak around 17 or 18 thousand years ago. Much of Canada and the northern part of the U.S. (especially the upper Midwest and the Northeast) were covered by continental glaciers. Alpine glaciers were extensive in the West. Northern Europe was similarly affected. After a few thousand years, the glaciers retreated and got roughly to their present positions by about six thousand years ago. There are going to be significant environmental changes occurring where glaciers cover the land (obviously) but the climate changed over much of the world during these times. Beyond the ice, there is a region of cold land referred to as a
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Glacial: 2 periglacial environment. Many parts of the world received more rainfall during glacial times, these are called pluvial periods . For example, there are rock paintings in the Sahara Desert showing the land as lush and rich in big game, like zebras and giraffes. In the arid West, where there is interior drainage, large lakes existed because precipitation was greater than evaporation. Death Valley had a large lake in it- the shorelines are still visible on the alluvial fans. Sea level dropped during glacial advances. It is believed that the North American Indians arrived on this continent during the last advance while there was a land bridge connecting Siberia and Alaska.
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