December 1, 2008

Iceberg computer program is created

U.S. scientists say they've created a computer program to help predict when icebergs will calve from ice sheets.

The models we have do not currently have any way to figure out where the big ice sheets end and where the ice calves off to form icebergs, said Penn State Professor Richard Alley.

The problem, he said, is the great variability involved in iceberg calving. One important variable -- the one that accounts for the largest portion of when the iceberg breaks -- is the rate at which ice shelves spread. When ice shelves spread, they crack because of the stresses of spreading. If they spread slowly, the cracks don't propagate through the entire shelf and the shelf remains intact, he said. If the shelf spreads rapidly, the cracks propagate through the shelf, thereby causing calving.

Spreading explains most of what is observed on the ice sheet, said Alley. However, the equations come out a little better if we include a few other things.

The researcher determined the basic equation for ice calving is the rate of spreading, times the width of the shelf, times the thickness, times a constant. The researchers said that equation doesn't capture the totality of variation in the ice calving process, but it does account for a large percentage of the variability.

The study appeared in the Nov. 28 issue of the journal Science.