About Glaciers and Pack Ice
More than 99 percent of Antarctica is covered with ice. This constitutes 90 percent of the world's ice and 70 percent of the world's freshwater. It has long been estimated that if all of Antarctica's ice were to melt, global sea levels would rise between 160 and 200 feet.
The Antarctic ice sheet can be as thick as 15,670 feet in places, raising Antarctica's average elevation to 7,500 feet above sea level, making Antarctica the highest of all the continents. Icebergs are formed where glaciers, ice sheets or ice shelves meet the ocean, and ice breaks, or calves, off into the sea. Nearly 350 cubic miles are lost from the Antarctic ice sheet a year, mainly due to icebergs calving into the sea.
As glaciers move downhill, they are stretched and twisted by the surrounding terrain. As this happens, the ice will split, and deep cracks, called crevasses, will be formed. These may reach up to several hundred feet deep. Crevasses present an extreme hazard to glacier travel, and many explorers, mountaineers, and skiers have been lost in their depths.
Some glaciers, called ice streams, do not travel over rock but move independently through the surrounding ice. The mechanisms for their existence are not fully understood. The Rutford Ice Stream descending from the Ellsworth Mountains into the Ronne Ice Shelf is an example.
Not all of Antarctica is covered with ice. The ice-free Dry Valleys in East Antarctica were formed when the underlying ground was uplifted at a faster rate than the glaciers could cut through them.
Despite all the ice, Antarctica is the driest continent on Earth: Less than 2 inches of precipitation falls as snow in the interior of the continent and less than 6 inches in the ice-free areas. The coldest temperature ever recorded on Earth has been in Antarctica: -89.6°C (-129.9°F) at Vostok Station in July 1983. Usual temperatures range from -70°C (-94°F) in winter in the interior to a balmy 0°C (+32°F) on the coast in summer.
Photo Credits: © 1999 WGBH, Photo: Kelly Tyler
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