By NED ROZELL
July 26, 2009
Part of the confusion may come from recent news of glacier advances in places like Icy Bay, where masses of ice have spilled deeper into the bay than they have for years. But an advancing glacier might not be a growing glacier. Such is the case in Icy Bay, according to Chris Larsen of the University of Alaska Fairbanks' Geophysical Institute.
"Even though they are
advancing, we have precise, recent laser data that shows the
glaciers in Icy Bay have the greatest thinning rates of anywhere
in Alaska," Larsen said.
"Terminus advance, in this case, is not a sign of a healthy glacier," he said "Quite the opposite."
Martin Truffer, also of the Geophysical Institute, just returned to Fairbanks from Yakutat Glacier, which is fading near the town of Yakutat on Alaska's gulf coast. Scientists in Alaska have several dependable methods for measuring glaciers, among them laser-altimetry systems mounted in planes that fly over glaciers, as well as gravity-measuring systems deployed by satellites. These methods have helped researchers find that most of Alaska's glaciers are on the wane, despite a snowy and cold 2007-2008.
"If you look at individual glaciers, you see a few that are gaining, but what counts is what the overall picture is," Truffer said. "Last year was a good year for glaciers in general, but take that in the context of many years of rapid retreats."
Bruce Molnia of the U.S. Geological Survey in Reston, Virginia, just flew over southern Alaska, taking photographs of glaciers in a project in which he compares images of glaciers to those from the past. He said glaciers that are above about 10,000 feet in elevation don't change much because the temperature there stays cold, but "99 percent of the 2,000 valley glaciers in Alaska are currently thinning, retreating, or melting in place."
In his recent flights along the coast of Alaska, Molnia said he did see a few advancing glaciers, and some of those are growing. Hubbard Glacier north of Yakutat is one of them.
Truffer and others say Hubbard is a tidewater glacier in the advancing phase of an advance-and-retreat cycle. The cycles of glaciers that calve into the sea are dependent upon dynamics of the sea floor and other complicated elements.
"It is true that there are several glaciers in Alaska that are advancing, but their advance has nothing to do with climate change," said Roman Motyka, a Geophysical Institute glaciologist who works out of Juneau. "In Southeast Alaska, over 90 percent of the glaciers are retreating and thinning, and the rates have accelerated in recent years."
"The general long-term
trend for glaciers in Alaska is one of sustained mass loss,"
said Shad O'Neal, A USGS glaciologist who also studies Icy Bay
glaciers and is based at the USGS Alaska Science Center in Anchorage.
"While we have seen short term fluctuations like a heavy
snow year and seasonal advance-retreat cycles, only a few tidewater
glaciers are gaining mass over longer time scales, and these
are exceptions, not the norm."
University of Alaska Fairbanks, in cooperation with the UAF research
community. Ned Rozell is a science writer at the institute.
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