Second giant ice island set to break off Greenland glacier

In August 2010, part of the Petermann Glacier about four times the size of Manhattan island broke off , prompting a hearing in Congress.

Researcher Alun Hubbard, of the Centre for Glaciology at Aberystwyth University, U.K., told msnbc.com by phone that another section, about twice the size of Manhattan, appeared close to breaking off.

In 2009, scientists installed GPS masts on the glacier to track its movement.

But when they returned in July this year, they found the ice had been melting so quickly — at an unexpected 16-and-a-half feet in two years — that some of the masts stuck into the glacier were no longer in position.

Hubbard, who has been working with Jason Box, of Ohio State University, and others, said in a statement issued by the Byrd Polar Research Center that scientists were still trying to work out how fast the glacier was moving and the effect on the ice sheet feeding the glacier.

But he said he was taken aback by the difference between 2009 and 2011 when he visited the glacier in late July.

"I'm very familiar with the glacier. It's very hard to sort of envisage something so big not being there ... to come back and basically see an ice shelf has disappeared, which is 20 kilometers across (about 12 miles) ... I was speechless and started laughing because I couldn't sort of believe it," Hubbard added, speaking to msnbc.com.

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