About Glaciers and Pack IceMore 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.
Glaciers
Glaciers are huge rivers of ice that flow down from the ice sheet in the
interior of the Antarctic continent. On their journey downhill, glaciers
carve depressions through the underlying rock and will exploit geological
features or weaknesses as they travel through mountain chains. The surface
of a glacier may provide a means of passage for explorers: Sir Ernest
Shackleton's discovery of the 124-mile-long Beardmore Glacier in 1908
opened one of the key routes from the Ross Ice Shelf to the polar plateau
of the interior.
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.
Pack Ice
Since Antarctica is in the Southern Hemisphere, its seasons are the opposite of
those of the Northern Hemisphere. During the Antarctic winter, the seas surrounding
the continent freeze, and this bed of pack ice grows from around 1 million square miles
to up to 7.3 million square miles by the end of the winter in September-October.
This variation is greater than the area of the Antarctic continent itself. In the Weddell
Sea, the thickness of this ice belt can reach up to 1,860 miles, and it was here that
Shackleton's Endurance was trapped and then crushed by the pack ice.
Photo Credits: © 1999 WGBH, Photo: Kelly Tyler
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