Klimaatverandering 68

'Ice Shelf Collapse Sends Chill.
By Margaret Munro.

Canada's North changing. Global warming suspected cause of huge breakup on Ellesmere Island.
An ancient ice shelf has cracked off northern Ellesmere Island, creating an enormous 66-square-kilometre ice island and leaving a trail of icy blocks in its wake.
"It really is incredible," said Warwick Vincent of Universite Laval, one of the few people to have laid eyes on the scene. "It's like a cruise missile has come down and hit the ice shelf."
The breakup was so powerful, earthquake monitors 250 kilometres away picked up the tremors as the 3,000- to 4,500-year-old shelf tore away from its fjord on Ellesmere.
It broke up 16 months ago, but no one was present to see it. The scientists say they are only now making public details after piecing together what occurred using seismic monitors and Canadian and U.S. satellites.
They say the ice shelf collapse, suspected to have been caused by global warming, is the biggest in Canada in 30 years and is indicative of the transformation under way on Ellesmere, Canada's most northern land mass.
"We are seeing incredible changes," said Vincent, whose group is studying the island's disappearing ice shelves and their unique ecosystems. "People talk of endangered animals - well, these are endangered landscape features and we're losing them."
The Ayles ice shelf was one of six ice shelves left in Canada, remnants of a vast icy fringe that used to cover the top end of Ellesmere.
Scientists consider the Canadian shelves, located about 800 kilometres south of the North Pole, sentinels that reflect the accelerating change in the Arctic.
In 2002, one of Vincent's graduate students, Derek Mueller, discovered that Ellesmere's Ward Hunt ice shelf had cracked in half. The researchers have also seen the sudden collapse of ice dams and the draining of 30-kilometre-long lakes into the sea.
The shelves are 90 per cent smaller than they were when Arctic explorer Robert Peary crossed them in 1906. And the Ayles ice shelf can be erased from Canada's maps.
"It no longer exists," Vincent said.
Laurie Weir, of the federal Canadian Ice Service in Ottawa, was poring over images from the RADARSAT satellite when she noticed the shelf had broken away. She passed the information on to Luke Copland, head of the new global ice lab at the
University of Ottawa, who led the effort to determine what had happened.
It turned out it took less than one hour for the ice shelf to calve off in the early afternoon of Aug. 13, 2005, Copland said. Low frequency "rumbling" and tremors were picked up on earthquake monitors, and Canadian and U.S. satellites captured images of the shelf cracking and breaking away.
"If you were standing right on the edge of the shelf, there'd have been this huge 15-kilometre crack as far as you could see in both directions," Copland said.
"And then the ice drifted off."'

Lees verder:
http://www.truthout.org/issues_06/122806EA.shtml Of: http://www.canada.com/montrealgazette/news/story.html?id=e4c99314-a71a-4418-a246-eea457e8b873&k=82636