Alaskan glacier aids study of world sea levels

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.

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