NewsJune 28, 2017

The Larsen C Rift is Racing to Its Conclusion

Brian Kahn

By Brian Kahn

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A rift has torn the Larsen C ice shelf asunder and now the outside edge of the ice is moving at an unprecedented pace. When it breaks off, it will become one of the largest icebergs ever recorded.

The crack is just eight miles away from breaking off what will likely be the second-biggest iceberg observed. The massive hunk of ice has already started to wiggle like a loose tooth. That includes ice near where the crack began, which is moving at an unprecedented speed of 33 feet per day. In the world of glacial-paced ice, that’s the equivalent of an all-out sprint.

Ice on the back end of the Larsen C crack is moving faster than it ever has before in another sign that calving is imminent. The images show ice shelf movement on the ocean side of the rift in early June (left) compared to late June (right).
Credit: Project MIDAS

“In another sign that the iceberg calving is imminent, the soon-to-be-iceberg part of Larsen C ice shelf has tripled in speed to more than 10 meters per day between 24th and 27th June 2017,” the scientists wrote on their Project MIDAS site. “The iceberg remains attached to the ice shelf, but its outer end is moving at the highest speed ever recorded on this ice shelf.”

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The speed-up is the latest sign that an iceberg is truly on the brink of forming. Project MIDAS researchers have been monitoring the state of the ice shelf since October 2015. During that time, they’ve observed periods of massive growth in the length of the crack across the ice shelf, widening to the point where you could lay the Empire State Building on its side to form a bridge across the chasm. More recently, a new branch sprouted, further warping the ice.

The latest change brings the break-off date that much closer to happening, though researchers cautioned it could still be weeks before the crack breaks through completely. When it does, though, it will drastically alter one of the largest ice shelves on the Antarctic Peninsula.

Scientists estimate that 10 percent of the ice shelf will break off, an area roughly as large as Delaware. That will change how the remaining ice shelf behaves, though it will take years of monitoring to see how those changes play out.

The Larsen C rift is driven by natural processes, but climate change could play a role in what comes next for the ice shelf, either from warm water undercutting what’s left of the ice shelf or warm air causing melt ponds on the surface. Both would weaken the remaining ice and make it more susceptible to melt and possibly collapse, though it will take years for researcher to tease those signals out.

“The area of ice about to be lost has a different stress regime to the central parts of the ice shelf,” Bethan Davies, an Antarctic ice researcher at Royal Holloway, University of London, said. “This change in stress regime may make calving easier and result in an increase in calving events. We will be watching this over the next few years.”

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