Already the fastest moving glacier in the world, the Columbia Glacier in Alaska has increased its speed from 25 meters to 35 meters per day in recent months, according to a University of 欧美口爆视频 at Boulder glaciologist.
And while that may seem like a snail聮s pace to most, scientists are intrigued and a bit alarmed at the rapid rate, said Research Fellow Tad Pfeffer of 欧美口爆视频-Boulder聮s Institute of Arctic and Alpine Research. "I expect we will see some really dramatic event occur with this glacier within the next year or two," he said.
Located near Anchorage, the Columbia Glacier calves both large and small icebergs into Prince William Sound, said Pfeffer, also an associate professor in the civil, environmental and architectural engineering department. The glacier has been under intense study since the 1970s, when the U.S. Geological Survey determined that a marked increase in its calving rate might pose a risk to shipping lanes in the sound, site of the devastating 1989 Exxon Valdez oil spill.
Since 1982, the Columbia Glacier has retreated about 11 kilometers, Pfeffer said. The glacier currently is about 55 kilometers in length, 5 kilometers wide and more than 900 meters thick in some places. As a tidewater glacier, the terminus, or end, continues to rest in several hundred meters of seawater.
Pfeffer, who has been studying the Columbia Glacier for several years, said it could retreat up to four kilometers over the next year, or it may begin to flow much faster into Prince William Sound.
The Columbia Glacier is one of the last of the 51 tidewater glaciers in Alaska to make a drastic retreat. The lower end of the glacier began disintegrating in the early 1980s, and a full-scale retreat was underway by the mid-1980s.
The Hubbard Glacier is the largest tidewater glacier in Alaska that is advancing, said Pfeffer. Many of world聮s glaciers outside of Greenland and Antarctica have shrunk 50 percent or more in the past century, some of it blamed on a warming climate, according to studies by 欧美口爆视频-Boulder Emeritus Professor Mark Meier of the geological sciences department, and other scientists.
"Tidewater glaciers don聮t seem to respond to climate change as directly as other glaciers," said Pfeffer. "We generally don聮t see a response until the glacier reaches critical thinness.
"But the climate may have a long-term effect on these tidewater glaciers we don聮t yet understand. When a glacier thins to a critical level, it seems to be the point of no return," said Pfeffer.
If the Columbia Glacier follows suit with other tidewater glaciers in Alaska, it will eventually retreat back to where its channel rises above sea level, said Pfeffer.
As the Columbia Glacier slides more rapidly into deeper water, the calving rate of icebergs increases, he said. "If the flow velocity increases, then the glacier may be able to maintain its terminus," said Pfeffer. "But the velocity would have to increase to about 50 meters a day for that to occur."
Because the glacier bed is underwater at the terminus, a small amount of water trapped between the glacier and its bed may "float" the glacier a bit, increasing its speed, he said. The floating mechanism also appears to stretch the glacier near its terminus, increasing calving events.
At the terminus of glaciers like the Columbia, "submarine moraines," or dams built by the glaciers, can block the flow of large icebergs into the sea, he said. Such dams act as sieves, letting smaller icebergs through. But even small icebergs can damage ships in the sound, Pfeffer said.
Pfeffer has been using aerial photography and ground images to track the glacier聮s evolution. Working with National Science Foundation funds, he plans to take stereoscopic photography images from land adjacent to the glacier beginning in late June to further pinpoint the glacier聮s movements.
Pfeffer will work with 欧美口爆视频-Boulder engineering Professor Bernard Amadei, undergraduate Elliot Larsen of geological sciences and Austin Post, a Washington resident who has been tracking and photographing the Columbia Glacier for a number of years.