Study predicts fewer icebergs from Alaska glacier

ANCHORAGE, Alaska — The rate of icebergs breaking off from Alaska’s Columbia Glacier will significantly slow within eight years, according to a new study.

Scientists from the University of Colorado at Boulder used a computer model that indicated the tidewater glacier by 2020 will retreat to a new, stable position in shallower water. The glacier, the study said, will achieve “dynamic equilibrium,” where the rate of ice accumulation equals the rate of ice ablation, or ice removal.

That should slow the dramatic discharge of ice into ocean water that started in the 1980s and accelerated with warming, the study’s authors said.

The Columbia Glacier is 95 miles east of Anchorage. It covers 425 square miles and was first documented in 1794 at 41 miles long.

A steady retreat began in the 1980s, said Steve Frenzel of the U.S. Geological Survey in Anchorage. The glacier not only lost ice as it retreated, he said, but also thinned considerably.

“It’s lost a huge volume of ice,” he said.

The glacier became a footnote to history in 1989 when the crude oil tanker Exxon Valdez changed course to avoid one of its icebergs and ran aground on Bligh Reef, spilling crude oil into Prince William Sound. The spill, however, trigged significant studies of Columbia Glacier calving, according to the study’s authors, and the glacier has become one of the most well-documented tidewater glaciers in the world.

By 1995, Columbia Glacier had shrunk to 36 miles long and by late 2000, it was down to 34 miles long, the study’s authors said.

By 2020, the study said, the Columbia Glacier will be just 26 miles long. The researchers conclude that the end of the glacier will have retreated into water shallow enough to provide a stable position through 2100.

The study was done in the context of rising sea levels.

“Presently, the Columbia Glacier is calving about 2 cubic miles of icebergs into the ocean each year — that is over five times more freshwater than the entire state of Alaska uses annually,” said lead author William Colgan in the study’s announcement. “It is astounding to watch.”

The expected decrease in calving, however, indicates how difficult it is to estimate rates of sea level rise, Colgan said. Many people believe glaciers’ contributions to sea level rise will be a predictable curve into the future that can be modeled for a century or more. However, a single glacier’s contribution to sea level rise can turn on and turn off, he said in the announcement. The study was published Monday in The Cryosphere, which is a publication of the European Geophysical Union.

“The variable nature and speed of the life cycle among glaciers highlights difficulties in trying to accurately predict the amount of sea level rise that will occur in the decades to come,” Colgan said.

Colgan could not be immediately reached by email. The study was funded by NASA.

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