Formerly Stable Greenland Glacier Now Retreating Rapidly

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"SAN FRANCISCO ­ One of the world’s fastest-moving glaciers is speeding up and retreating rapidly, a recent study has revealed. The finding has surprised scientists, because while the margins of the Jakobshavn (pronounced “yah-cub-SAH-ven”) Glacier had been slowly retreating from the southwest coast of Greenland since before 1900, this retreat appeared to have stopped by the early 1990s when the first accurate measurements were made. Now the glacier is accelerating.

The glacier, one of the major drainage outlets of Greenland’s interior ice sheet, is thinning more than four times faster than it had for most of the 20th Century. Accompanying this thinning is a substantial increase in ice speed.

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Scientists believe that Jakobshavn remained unchanged until 1900, when the ice surface near the calving front began lowering by 2.5 meters (about 8 feet) per year on average. According to the new data collected by NASA’s Airborne Topographic Mapper laser system, the glacier was slightly thickening between 1991 and 1999, before it started to thin rapidly. Current thinning rates have reached 12 meters (about 39 feet) per year.

That’s probably because the Jakobshavn Glacier, which was flowing at 7 kilometers (about 4.4 miles) per year, is now flowing at 9 kilometers (about 5.6 miles) per year, said Kees van der Veen, visiting associate professor of geological sciences and research scientist at BPRC."

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http://researchnews.osu.edu/archive/greenice.htm