Images released by NASA on Wednesday showed the huge chunk of ice - twice the size of Manhattan - separating from the Petermann Glacier and moving downstream along a fjord on Greenland's northwest coast.

It is the second time in less than two years that the Petermann Glacier has released a massive iceberg.

In 2010, another ice island 'calved' from the glacier, entering North Atlantic shipping lanes but causing no damage, according to Trudy Wohlleben of the Canadian Ice Service.

"At this time of year, we're always watching the Petermann Glacier," Wohlleben said, citing the danger to shipping.

NASA said the crack in the glacier had first been identified in 2001, but that its Aqua satellite had then seen the break occur on July 16-17.

Climate change implicated

Andreas Muenchow, an Arctic oceanographer at the University of Delaware, said climate change was a factor in the current state of the Petermann Glacier.

Speaking by telephone with the Reuters news agency, Muenchow said the current break could cause the glacier to move toward the sea even faster, after the 2010 break had already accelerated its motion by 10 to 20 percent.

The separation of an iceberg can speed up a glacier's seaward movement, as such chunks of ice, while still anchored, can act as obstructions to its motion.

Muenchow said that the Atlantic waters melting the glacier appear to be warming, but that records only go back to 2003.

"Some changes are dramatically visible, such as the discharge of large ice islands, " he wrote on his blog at icyseas.org. "Some changes, perhaps more important, are not."

tj/msh (Reuters, AFP)