By AScribe Newswire
BOULDER, Colorado—Alaska's
Columbia Glacier, heralded as the world's speediest 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 glacier
continues to move at speeds of up to 34 meters a day, a snail's
pace to most but astoundingly swift to glaciologists, said Tad
Pfeffer, a fellow of CU-Boulder's Institute of Arctic and Alpine
Research. Descending from the Chugach Mountains into Prince Williams
Sound near Valdez, the Columbia Glacier has retreated about 12
kilometers since 1982 and thinned significantly in that time.
"The
glacier is calving icebergs into Prince Williams Sound much faster
than it is accumulating new snow," said Pfeffer, an associate
professor in civil, environmental and architectural engineering.
"It is spending its capital, in effect. 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 stayed in roughly the same place for the
past year, its bottom resting on bedrock about 500 to 550 meters
below sea level, said Pfeffer. The Columbia Glacier is the last
of Alaska's 51 tidewater glaciers to begin a drastic retreat.
CU-Boulder
and the U.S. Geological Survey have been monitoring changes in
the glacier in the last several decades, using field observations,
aerial photography and numerical modeling. Since 1976, 117 photo
flights have been made over the glacier by researchers, who also
use satellite images to track its movements, Pfeffer said.
Pfeffer is
the chief author of a paper on the Columbia Glacier to appear
in the Nov. 28 issue of Eos, an international weekly newspaper
on geophysics published by the American Geophysical Union in Washington,
D.C. Co-authors on the paper include CU-Boulder emeritus Professor
Mark Meier of geological sciences, CU-Boulder graduate student
Josh Cohn, and USGS scientist Robert Krimmel.
The Columbia
Glacier currently 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
by Cohn 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, Pfeffer
said.
The Columbia
Glacier is expected to eventually retreat as far as 25 kilometers
up the glacial valley to a point equal to sea level. "It
should be quite a spectacular sight in the not too distant future,"
said Pfeffer. "We intend to follow the process very closely."
Unlike well-known
glaciers nearer the equator -- 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 intimately tied to the rapid
changes of the glacier and of the world's large ice sheets, he
said.
"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."
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