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Alaskan glacier races forward.

The term "glacial" can describe the pace of lines at the Post Office or the plodding progress of Congress. But there's nothing slow about the speed of the Bering Glacier, the largest stream of ice on the North American continent. Last spring, a small patch of the glacier dramatically accelerated its normally stately flow downslope (SN: 8/7/93, p.95). Since then, the surging region has spread to include half the 5,175-square-kilometer surface area of the glacier, says Bruce F. Molnia of the U.S. Geological survey in Reston, Va.

The surge started in the middle of the glacier and expanded from there until it reached the end of the Bering in late August. Photos taken by airplane on July 10 (top) and September 10 (bottom) show the advance of the glacier's terminus (arrow), which moved forward more than 1,500 meters in just three weeks, spreading into part of Vitus Lake at the end of the glacier. In late August and early September, the glacier's foot marched forward at speeds approaching 100 meters per day, nearly 100 times its normal pace. Ice calving off the terminus has filled much of Vitus Lake with icebergs, which appear white in the pictures.

The glacier has surged roughly once every two decades during the 20th century, with the last such event ending in 1967. Studies on smaller glaciers suggest that they surge when the plumbing system below the ice gets clogged with silt. Water that normally flows out from under a glacier then accumulates beneath the ice, eventually lifting it off the bedrock. That reduces friction between the ice and ground, sending the glacier sliding downhill.

Since they don't have instruments set up under the Bering Glacier, scientists can't be sure that the same process caused points in that direction there. But some circumstantial evidence points in that direction.

Molnia says clients studying the glacier and pilots flying over it this year have noted large numbers of ephemeral lakes on the surface of the ice, suggesting that the drainage system through the glacier has become plugged.

Past surges of the Bering Glacier have lasted about 18 months and have, at times, filled virtually all of the Vitus Lake basin with ice. Once the glacier slows, its foot retreats back-up-slope, reopening the lake basin.
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Title Annotation:Bering Glacier moves over 1,500 meters in three weeks
Publication:Science News
Article Type:Brief Article
Date:Nov 20, 1993
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