Alaska's fast-moving Columbia Glacier melts into fjord
December 4, 2000
Alaska's Columbia Glacier appears to be on a course to disintegrate and evolve into a spectacular fjord rivaling Glacier Bay in the coming years, according to a University of Colorado at Boulder researcher.
The Columbia Glacier is the last of Alaska's 51 tidewater glaciers to begin a drastic retreat.
The glacier continues to move at speeds of up to 34 meters a day - a swift rate to glaciologists. Descending from the Chugach Mountains into Prince Williams Sound near Valdez, the Columbia Glacier has retreated about 12 kilometers since 1982 and has thinned significantly.
"The glacier is calving icebergs into Prince Williams Sound much faster than it is accumulating new snow," said Tad Pfeffer, a fellow of CU-Boulder's Institute of Arctic and Alpine Research. "The glacier either will retreat rapidly up the fjord or thin rapidly and essentially disintegrate in an abrupt event."
The glacier's terminus, or toe, has remained in roughly the same place for the past year, its bottom resting on bedrock about 500 to 550 meters below sea level.
Using field observations, aerial photography and numerical modeling, CU-Boulder and the U.S. Geological Survey have been monitoring changes in the glacier for the last several decades. Since 1976, 117 photo flights have been made over the glacier by researchers, who also use satellite images to track its movements.
Pfeffer is the chief author of a paper on the Columbia Glacier that appeared in the Nov. 28, 2000 issue of Eos, an international weekly newspaper on geophysics published by the American Geophysical Union.
The Columbia Glacier is about 54 kilometers long, 5 kilometers wide and more than 1,000 meters thick in some places. Because the glacier bed is underwater at its terminus, water pressure floats it slightly, increasing its speed and stretching the terminus like a piece of taffy. The glacier's thinning and mass loss in recent years have caused more frequent calving of icebergs.
The rapid flow and calving began in 1982, and the terminus has been stretching as much as 1.5 percent per day, said Pfeffer. Modeling calculations have shown the terminus will continue its retreat upstream in the coming years, where the glacier bed drops to as deep as 700 meters below sea level.
As the terminus retreats into the deepening glacial bed, the researchers expect significantly increased calving into Prince William Sound.
The Columbia Glacier is expected to eventually retreat as far as 25 kilometers up the glacial valley to a point equal to sea level.
Unlike other well-known glaciers - including those in the Alps, which have lost about 50 percent of their mass in the past century - glaciers in Alaska have not been studied in depth regarding their response to a warming climate, said Pfeffer. While the Columbia Glacier retreat is not an immediate consequence of warming since neighboring glaciers do not show the same dramatic behavior, the coupled glacier-ocean system may be tied to the rapid changes of the glacier and of the world's large ice sheets, according to Pfeffer.
"The loss of ice primarily is due to calving rather than to thermal reasons," said Pfeffer, who took stereoscopic images of the Columbia Glacier from aircraft and nearby land points last summer to chart its behavior. One reason scientists are watching the Columbia Glacier closely is that icebergs calved into Prince William Sound pose a potential hazard to ships, although the glacier terminus has carved an underwater shoal of rocks and sediment that act as a dam to block the flow of large icebergs into the sound.
Pfeffer predicted the Columbia Glacier may well be transformed into a large fjord within 50 years and perhaps in less than a decade. "We don't know enough about the physics of tidewater glaciers yet," he said. "But I think we may be seeing tour boats where the glacier is presently sitting in the not too distant future."