A crack in the Larson C ice shelf reached within 8 miles (13 kilometers) of the ocean after expanding 11 miles (17 kilometers) in just the last week, scientists with Project MIDAS at the University of Swansea in Britain said on Thursday.

Scientist studying the region expect the 1,900-square-mile (5,000-square-kilometer) chunk of ice to separate from the Larson C ice shelf within weeks. An ice shelf is a sheet of ice floating over the ocean.

If and when it does, the Larcon C ice shelf would be 10 percent smaller, reducing it to the smallest size ever recorded.

"The rift in Larsen C is likely to lead to one of the largest icebergs ever recorded," said Swansea University in Wales.

Scientists say the iceberg itself would not raise global sea levels, but it could cause the Larsen C ice shelf, Antartica's fourth largest, to become unstable and collapse.

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Two smaller, more northern shelves have already collapsed.

The Larsen A disappeared in 1995, and seven years later the Larsen B collapsed.

"We have previously shown that the new configuration will be less stable than it was prior to the rift, and that Larsen C may eventually follow the example of its neighbour Larsen B, which disintegrated in 2002 following a similar rift-induced calving event," the scientists with Project MIDAS said.

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The rift in the Larsen C ice shelf is hundreds of kilometers long.

The role of global warming

While icebergs are normal, scientists attribute the collapse or retreat of several ice shelves in recent decades to global warming.

"It is widely accepted that warming ocean and atmospheric temperatures have been a factor in earlier disintegrations of ice shelves elsewhere on the Antarctic Peninsula," Swansea scientists said.

The collapse of the Larsen C ice shelf would take possibly decades and contribute to a several centimeter rise in ocean levels.

"If Larsen C were to collapse, it would be concerning for its own reasons, but the contribution to global sea level rise would be very small, something in the centimeters," Dan McGrath, a scientist with the US Geological Survey, told Reuters.

More worrisome is that the collapse of ice shelves could destabilize glaciers in Western Antarctica.

The West Antarctic ice sheet holds enough frozen water to raise sea levels by about six meters (20 feet).

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cw/bw (AFP, AP, Reuters)