Antarctic ice shelf breaks

WASHINGTON — A chunk of Antarctic ice about seven times the size of Manhattan suddenly collapsed, putting an even greater portion of glacial ice at risk, scientists said Tuesday.

Satellite images show the disintegration of a 160-square-mile chunk in western Antarctica that started Feb. 28. It was the edge of the Wilkins ice shelf and has been there for hundreds of years, maybe 1,500.

This is the result of global warming, said British Antarctic Survey scientist David Vaughan.

Because scientists noticed satellite images within hours, they diverted satellite cameras and flew an airplane over the collapse for pictures and video.

"It's an event we don't get to see very often," said Ted Scambos, lead scientist at the National Snow and Ice Data Center in Boulder, Colo. "The cracks fill with water and slice off and topple ... That gets to be a runaway situation."

While icebergs naturally break away from the mainland, collapses like this are unusual but have been happening more frequently in recent decades, Vaughan said.

The rest of the Wilkins ice shelf, which is about the size of Connecticut, is holding on by a narrow beam of thin ice. Scientists worry that it, too, may collapse. Larger ice collapses occurred in 2002 and 1995.

Vaughan had predicted the Wilkins shelf would collapse in about 15 years. The part that recently gave way makes up about 4 percent of the overall shelf, but it's an important part that can trigger further collapse.

Scientists said they are not concerned about a rise in sea level from the latest event.

Climate in Antarctica is complicated. Much of the continent is not warming and some parts are even cooling, Vaughan said. However, the western peninsula, which includes the Wilkins ice shelf, juts into the ocean and is warming. This is the part of the continent where scientists are most concerned the melting ice would raise the sea level.