huge sheet breaks off canada ice shelf

A chunk of ice about 18 kilometres square has broken off Canada's largest remaining ice shelf, Officials say.

Trent University researcher Derek Mueller said he wouldn't be surprised if more ice broke off this summer from the Ward Hunt Ice Shelf, a vast frozen plain off the north coast of Ellesmere Island, in Canada's far north.

In a development consistent with climate change theories, the enormous icy plain broke free some time last week and began slowly drifting into the Arctic Ocean. The piece had been a part of the shelf for 3000 years.

A crack in the shelf was first spotted in 2002. Last spring, a patrol of Canadian Rangers found the weakness had spread into an extensive network of cracks, some 40 metres wide and 18 kilometres long. The crack-riddled section of ice was like a jigsaw puzzle, with the pieces held in place only by each other.

Formed by accumulating snow and freezing meltwater, ice shelves are large platforms of thick, ancient sea ice that float on the ocean's surface. Ellesmere Island was once entirely ringed by a single enormous ice shelf that broke up in the early 1900s.

At 440 square kilometres in size and 40 metres thick, the Ward Hunt shelf is the largest of those remnants - even bigger than theAntarctic shelf that collapsed earlier this year and seven times the size of the Ayles Ice Shelf chunk that broke off in 2005 from Ellesmere's western coast..................
http://www.theage.com.au/world/huge-sheet-breaks-off-canada-ice-shelf-20080730-3n9j.html