climate change

Watching glaciers slide—in a freezer

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Neal Iverson worked with a team of engineers to develop a machine that can simulate how glaciers slide across their beds. At the bottom of the machine is a hydraulic press that can create pressures equal to those beneath a glacier 1,300 feet thick. (Credit: Bob Elbert)

IOWA STATE (US)—A walk-in freezer in Iowa may help scientists understand how glaciers react to climate change and contribute to rising sea levels.

Neal Iverson, professor of geological and atmospheric sciences at Iowa State University, has worked for three years on his glacier sliding simulator, that is over nine feet tall.

At the center of the machine is a ring of ice about eight inches thick and about three feet across. Below the ice is a hydraulic press that can put as much as 170 tons of force on the ice, creating pressures equal to those beneath a glacier 1,300 feet thick. Above are motors that can rotate the ice ring at its centerline at speeds of 100 to 7,000 feet per year. Either the speed of the ice or the stress dragging it forward can be controlled.

Around the ice is circulating fluid—its temperature controlled to 1/100th of a degree Celsius—that keeps the ice at its melting point so it slides on a thin film of water. As Iverson starts running experiments with the simulator this month, he’ll be looking for data that help explain glacier movement.

“For a particular stress, which depends on a glacier’s size and shape, we’d like to know how fast a glacier will slide,” Iverson says.

Glacier sliding is something that matters far from the ice fields. The warmer the climate, the faster glaciers slide. When they hit coasts, they dump ice into the ocean. And when those icebergs melt they contribute to rising sea levels. But there’s a lot about the process researchers still don’t know.

“We can’t predict how fast glaciers slide—even to a factor of 10,” Iverson says. “We don’t know enough about how they slide to do that.”

So Iverson came up with the idea of a glacier in a freezer that allows him to isolate effects of stress, temperature and melt-water on speeds of glacier sliding. Still, the machine won’t simulate everything about glacier sliding.

“The fact is we can’t simulate the real process,” he explains. “We can only simulate key elements of the process. The purpose of these experiments will be to idealize how the system works and thereby learn fundamentals of the sliding process that can’t be learned in the field because of the complexity there.”

Iverson, who also does field studies at glaciers in Sweden and Norway, says glaciology needs work on the ground and in the lab. But, he says, it’s been decades since anybody has attempted the kind of laboratory simulations he’ll be doing.
“There hasn’t been a device to do this,” Iverson says. “And so there haven’t been any experiments.”

The project is supported by a grant from the National Science Foundation.

Iowa State University news: www.news.iastate.edu/

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