'Worrisome' cracks in glacier

2008-08-22 11:29

Washington - In northern Greenland, a part of the Arctic that had seemed immune from global warming, new satellite images show a growing giant crack and a 28.5-square-kilometre chunk of ice haemorrhaging off a major glacier, scientists said on Thursday.

It has led the university professor who spotted the wounds in the massive Petermann glacier to predict disintegration of a major portion of the Northern Hemisphere's largest floating glacier within the year.

If it does worsen and other northern Greenland glaciers melt faster, then it could speed up sea level rise, already increasing because of melt in southern Greenland.

The crack is 11km long and 1km wide. It is about half the width of the 1 300-square-kilometres floating part of the glacier. Other smaller fractures can be seen in images of the ice tongue, a long narrow sliver of the glacier.

Pictures speak for themselves

"The pictures speak for themselves," said Jason Box, a glacier expert at the Byrd Polar Research Centre at Ohio State University. He spotted the changes while studying new satellite images. "This crack is moving, and moving closer and closer to the front. It's just a matter of time till a much larger piece is going to break off. ... It is imminent."

The chunk that came off the glacier between July 10 and July 24 is about half the size of Manhattan Island in New York City and does not worry Box as much as the cracks. The Petermann glacier had a larger breakaway ice chunk in 2000. But the overall picture worries some scientists.

"As we see this phenomenon occurring farther and farther north, and Petermann is as far north as you can get, it certainly adds to the concern," said Waleed Abdalati, director of the Centre for the Study of Earth from Space at the University of Colorado.

The question that now faces scientists is: Are the fractures part of normal glacier stress or are they the beginning of the effects of global warming?

"It certainly is a major event," said Nasa ice scientist Jay Zwally in a telephone interview from a conference on glaciers in Ireland. "It's a signal, but we don't know what it means."

It is too early to say it is clearly global warming, Zwally said. Scientists do not like to attribute single events to global warming, but often they say such events fit a pattern.

'Not alarming'

University of Colorado professor Konrad Steffen, who returned from Greenland on Wednesday and has studied the Petermann glacier in the past, said that what Box saw is not too different from what he saw in the 1990s: "The crack is not alarming. ... I would say it is normal."

However, scientists note that it fits with the trend of melting glacial ice they first saw in the southern part of the massive island and seems to be marching north with time. Big cracks and breakaway pieces are foreboding signs of what is ahead.

Further south in Greenland, Box's satellite images show that the Jakobshavn glacier, the fastest retreating glacier in the world, set new records for how far it has moved inland.

That worries Colorado's Abdalati. "It could go back for miles and miles, and there's no real mechanism to stop it," he said.

- AP