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Columbia Glacier´s floating arm aids sea-level forecast

United States
Anchorage Daily News
09/08/2010
Rosemary Shinohara


Columbia Glacier in Prince William Sound, once grounded on the ocean floor, three years ago spawned a floating arm, say scientists who have been studying it.


As a result, the glacier began shedding chunks of ice almost the size of Midtown Anchorage, said Shad O'Neel, a U.S. Geological Survey glaciologist. But it may only happen once a week or so. "It's incredibly variable, with no real rhythm to it," said O'Neel. The glacier will be quiet. Then, "You'll suddenly have a calving event that's absolutely enormous."

Afterward, a section of the glacier a kilometer wide might be missing, he said.

That's a dramatic shift from its old pattern of calving, which consisted of dropping small-to-medium sized icebergs around five times an hour.

The more recent giant icebergs are highly fractured by the time they crash into the sea. They disintegrate immediately, so the glacier is not tossing monstrous obstacles into oil tanker and other shipping lanes.

But Columbia's changed calving behavior does have worldwide significance. It is a piece of the information scientists need to forecast the rise in sea levels around the globe.

O'Neel and other scientists' observations of Columbia Glacier mark the first time anyone has recorded the development of a large floating extension of an Alaska glacier that lasts for years.

CALVING HUGE CHUNKS

Their findings appear in a paper accepted for publication Saturday in the journal "Geophysical Research Letters." Fabian Walter of the Scripps Institution of Oceanography at the University of California, San Diego, led the study.

Columbia Glacier developed the floating extension in 2007.

Scientists had begun looking at its calving mechanism three years before that.

They installed time-lapse cameras and a network of seismometers, a sensor that measures ground vibrations from any sort of shaking, like an earthquake or calving.

They got seismic information over two periods: June 2004 to September 2005 and June 2008 to now.

The combined information has allowed them to document changes in the glacier before and after it had the floating extension.
Icebergs that are shed now can be up to 1 to 1 1/2 square kilometers when they break off, or the size of the square between Seward and C Street and Northern

Lights and Tudor, said O'Neel. That's five to 10 times bigger than they used to be, he said.

RAPID RETREAT

Columbia Glacier, the largest glacier in Prince William Sound, flows south from the Chugach Mountains to tidewater.

It has been in rapid retreat since about 1982.

Typically, said O'Neel, a tidewater glacier advances over thousands of years, then retreats over a matter of decades.

The researchers think the floating extension may have been created as a result of the fast speed with which Columbia Glacier is retreating.

Stan Stephens of Stan Stephens Cruises and Wildlife trips in Valdez has been visiting Columbia Glacier since 1961, and started doing tours into Columbia in 1978.

"The amount of ice is mind-boggling," Stephens said. "The whole arm will be solid full of ice."

Back in the early 1980s, you could take a boat to within a quarter-mile of the glacier, said Stephens. "We'd sit there for about an hour and watch it calve."

Then the amount of ice in the water increased, and you could only get within half a mile, then a mile. "Sometimes we couldn't get near it."

Now Stephens' cruises only get to about 12 miles away from the glacier. "All we look at is massive icebergs."

CLUE ABOUT RISING SEAS

Walter said in an e-mail that the scientists cannot draw any conclusions about whether the larger-sized icebergs that accompanied development of the floating extension have increased shipping hazards, since they splinter apart upon calving.

O'Neel said most of the ice stays within Columbia Bay, in the shallow water of the moraine at the toe of the glacier.

What's next for Columbia Glacier? It looks like much of the floating tongue has already broken off, said O'Neel.

The report on how ice calves from floating vs. grounded glaciers is expected to help scientists around the world figure out how to better forecast rising sea levels.
A rise in sea level matters because more than 100 million people live within about three feet of sea level, he said, such as people in New Orleans, and Bangkok, Thailand.

Melting of glaciers and calving of icebergs add water to the ocean that results in sea level rise, O'Neel said.

Scientists want to create a mathematical model that tells what all of the ice sheet and glaciers on the planet will do given certain climate changes, he said. Information on iceberg calving fits into the model.

"Our little piece goes in to help."

“Biodiversidad, deforestación y calentamiento global: en el 2100 sobrevivirán solamente entre el 18 y el 45% de las especies tropicales que conocemos”, Greenreport.it, Italia, 06/08/10:

 

The news content in this section is responsibility of the information agencies and does not necessarily reflect the position of the Government of Mexico on this or other related topics.

El contenido de las noticias que se presentan en esta sección es responsabilidad directa de las agencias emisoras de noticias y no necesariamente reflejan la posición del Gobierno de México en este u otros temas relacionados.

    

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