LYCOS RETRIEVER 
Glaciers
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Glaciers are heavy ice forms that are found at the North and South Poles or on high mountain tops. They are formed when layers of snow fall in an area that has temperatures way above freezing all year long. Snow layers fall one year, never melt, and new snow falls on top of the old snow until it is stacked up very high. After many years the older snow is flattened by the weight of the snow on top and becomes ice. Eventually the snow piles up high enough to form a glacier. When the glacier forms over an area that has a slope, gravity pulls it down the slope. Glaciers grow to be many miles long, and in some places glaciers are almost a mile high. Glaciers hold more than one-half of the fresh water on earth today.
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Glaciers are big conveyors, moving ice and rock from a high-elevation accumulation zone to a lower-elevation ablation zone. The accumulation zone is that part of the glacier, ice cap, or ice sheet on which the prior winter's snow persists through the summer season. In the ablation zone, summertime melting removes the winter snow and perhaps some of the underlying glacier ice as well. The boundary between the areas of net accumulation and net ablation at the end of the summer season is called the equilibrium line. The downstream terminus (end point) of a glacier is found where the rate of ice flow is equal to the rate of ablation. Where the glacier ends in the ocean or a lake, mass ... is lost to iceberg calving.
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Glaciers on Iceland had their maximum Little Ice Age extension by 1890-1920. Glacier variations in Iceland since 1930 show a clear response to variations in climate during this period: Most non-surging glaciers retreated strongly during the early half of the monitoring period, following the warm climate between 1930 and 1940. A cooling climate after 1940 led to a slowing of the retreat and many glaciers started to advance around 1970. Warming climate since 1985 led to an increased number of retreating glaciers, and all Icelandic outlet glaciers are retreating presently and the ice caps are loosing ice volumes due to accelerating summer melt (Figure 12). The estimated coverage loss per year is about 0.2% overall, which amounts to 20-30 km2 becoming ice free every year. If the present trend continues, most glaciers on Iceland will have melted away within 500 years.
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Glaciers in the Rocky Mountains and Western Coastal Ranges have experienced considerable losses during this century, and melting is accelerating rapidly in southern Alaska. Since Glacier National Park (Montana, USA) was established in 1910, more than two thirds of its glaciers and about 75% of its glacier area has disappeared29; if the present rate of warming continues, there will be no glaciers left in the Park by 2030 (30). In Banff, Jasper, and Yoho National Parks in the Canadian Rockies, glacier cover has decreased by at least 25% during the 20th century (31). South Cascade Glacier in coastal Washington (USA) lost 19 m of ice thickness between 1976 and 1995, ten times more than during the previous 18 years (32). Nearly all glaciers surveyed in Alaska are melting, and thinning rates in the last 5-7 years are more than twice those seen in previous decades (13).
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Glaciers form when snow accumulates on a patch of land over tens to hundreds of years. The snow eventually becomes so thick that it collapses under its own weight and forms dense glacial ice. When enough of the ice is compacted together it succumbs to gravity and begins to flow downhill or spread out across flat lands (Williams and Hall, 1993). There are many different types of glaciers, and not all of them are good indicators of climate change. "Glaciers that do tend to be good climate indicators are small land-based, non-surge type glaciers. They respond directly to both regional temperature and precipitation [snow]," said Dorothy Hall, a hydrospheric scientist at NASA’s Goddard Flight Space Center. She and a team of scientists from around the globe have used satellites over the past 25 years to measure changes in glaciers in Europe, Iceland and Alaska.
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Glaciers have long played a role in the geologic history of California. In the past, glaciers were active in several areas of California leaving behind geologic evidence such as glacial deposits, mountain cirques, and glacial striations. In northern California, evidence from glaciers during the Pleistocene is found at Mount Shasta, Lassen Volcano, and throughout the Klamath Mountains, Medicine Lake Volcano, Salmon Mountains, Warner Mountains, and some in the Coast ranges. In central California evidence from glaciers can be found in the Sierra Nevada, White Mountains, and in the Sweetwater Range. The only evidence in southern California has been found in the San Bernardino Mountains (Sharp at al, 1959).
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