there are glaciers in all areas of the globe. Most glaciers are found in the polar regions, but many of the Earth's tallest mountains also have glaciers. Glaciers go through life cycles. They have growing years, moving years, and retreating years. For glaciers to form, very specific climatic conditions are necessary. They are usually found where there is enough snowfall for a snow pack to permanently accumulate, where summers are not warm enough for all of the snow to melt. In some regions, such as at the North Pole, the intense cold squeezes out moisture as rain or snow before it advances to the far north. This makes the Arctic region a cold desert because the cold prevents the accumulation of snow. However, in warmer areas, the greater amount of moisture combined with sufficiently low temperatures encourage snow and the possibility of glacier formation.
There are two major kinds of glaciers: continental glaciers and valley glaciers. Continental glaciers are often called ice sheets—the glaciers in Antarctica are continental ice sheets. For practical purposes, the entire continent is locked in a single combined glacier. It is also a slow growth glacier because the low level of moisture adds only small amounts of snow each year. Alpine glaciers form in high mountain areas. In Africa, Mount Kilimanjaro has a glacial field. There are many other glacial areas such as those in the mountains of western North America and South America. New Zealand's South Island has glaciers, as do the Himalayas and the Alps in Europe.
Glaciers form because every year more snow remains than there was the previous year, because not all snow melts during the summer. As the winter snow accumulates, its weight turns the snow beneath it into ice. The snow that remains is called firn. As more snow falls, it and the snow above it compress the firn into buried layers that become thickened masses of ice crystals. In the second phase of glacier life, they move or flow. The sheer weight of the ice causes continental glaciers to move outward from a central point. As the ice is deformed internally by the weight of the ice above it, a thin layer of water forms at the bottom and the glacier then follows gravity's pull down the path of least resistance. The water may be from summer melt or from the pressure.
If the mountain slopes upon which a glacier has formed are steep, its movement may be rapid. The moving ice has internal stresses that cause fracturing into cracks (crevasses) that form at the surface of the glacier. Moving glaciers also have a dramatic impact on the environment. They scour the surface beneath them and scrape the sides of the mountain where they are flowing like frozen rivers. They crush rocks into pebbles and soil. As a glacier passes, there is erosion and then deposition of the glacial debris as moraines, drumlins, and eskers. Glaciers eventually melt and leave behind rocky debris. They also leave scoured areas, valleys, and mountainsides. The causes of glacial retreat are increases in temperatures, evaporation rates, and wind scouring that promotes sublimation. In the summertime, glaciers undergo a natural retreat in the form of ablation. A glacier will grow and move as long as more snow accumulates than melts. When there is more melting than accumulation, the glacier will eventually decrease in size or disappear.
In the northern part of North America, the glacial remnants of the last ice age are visible in many places. From New York to Labrador in the east, there are scoured mountain valleys and mountaintops. In the midwestern states and provinces, the lines of moraines and other glacial debris deposits can easily be seen from the air. Farmers as far south as Iowa plow in fields that are composed of glacial soil and where composts are easily seen. The shores of the Great Lakes provide other evidence of previous glacial activity. The retreat of the glaciers since the last Ice Age has continued slowly, until recently. Today, there is evidence of rapid melting in the alpine glaciers. The snows of Mount Kilimanjaro may disappear by 2030 if the melting continues. Other alpine glaciers in North America and in many other locations are also in retreat.
The alpine glaciers seem to be melting the fastest because they are the smallest and the most exposed to the global rise in temperatures. For example, the Franz Josef Glacier in New Zealand retreated rapidly over a 15-year period during the 1950s and 1960s. Other glaciers are also in rapid retreat such as the Quelccaya, Huascaran, and Chacaltaya glaciers in the Andes. Glaciers on tropical mountaintops are among the retreating glaciers. Photographic evidence, from as recently as 10-50 years ago, provides irrefutable proof that glaciers are retreating rapidly. The retreat of glaciers threatens the world's water supplies because snowmelt from mountain glaciers will be reduced when the glaciers are gone. The loss would also mean the loss of species that have adapted to cold water. Fish and plant that are used for food would be lost as well. Also, if the continental glaciers melt, sea levels will rise.
SEE ALSO: Glaciology; Ice Ages; Ice Albedo Feedback; Ice Component of Models.
BIBLIOGRAPHY. Michael Hambrey and Jurg Alean, Glaciers (Cambridge University Press, 2004); P.G. Knight, ed., Glacier Science and Environmental Change (John Wiley & Sons, 2006); Atle Nesje and S.O. Dahl, Glaciers and Environmental Change (A Hodder Arnold Production, 2000); B.S. Orlove, Ellen Wiegandt, and B.H. Luckman, Darkening Peaks: Glacier Retreat, Science and Society (University of California Press, 2008); Frank Sirocko, et al., eds,. The Climate of Past Interglacials (Elsevier Science & Technology Books, 2007).
Andrew J. Waskey Dalton State College
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