An Antarctic Iceberg the Size of Delaware Could Break Off in a Matter of Weeks

A fast-growing crack in the Larsen C ice shelf signals the accelerating changes underway on the southernmost continent.

Scientists are eyeing a growing crack in one of Antarctica's ice shelves. A portion of the Larcen C shelf the size of Delaware could break off in months, or even weeks - an event that could signal the impending collapse of another of the southernmost continent's ice shelves and an ominous sign of the impacts of a warming planet.

While that wouldn't contribute to sea level rise around the world, ice shelves act as breaks for the flow of land ice, which lies behind them. Without ice shelves in their paths, glaciers slide more easily into the oceans, which would push up global sea levels.

The crack in the Larsen C shelf, already more than 100 miles long and slicing through 820 feet of ice, grew another six miles in just three weeks last month. Only 12 miles of ice connects the portion that's at risk of breaking off from the rest of the shelf.

James White, director of the Institute of Arctic and Alpine Research at the University of Colorado Boulder, speculates that the calving event may occur very soon.

"Given how fast it's grown and how wide it is and how close it is to the coast and close to snapping off and isolating a big old chunk of ice it's more a question of weeks to months," he said. "I don't think it's years, but predicting that comes under the realm of sorcery."

White added that scientists don't fully understand ice shelf dynamics, but there's concern that once they begin to break apart, their collapse may be just around the corner.

"If you lose pieces like this then you get closer and closer to collapse and destruction of the entire ice shelf," White said.

A calving event followed by total ice sheet collapse is what happened with the Larsen A and B shelves, which sat north of Larsen C, in 1995 and 2002.

"[Larsen C ] is a very visible, very tangible, very predictable result of a warmer and warmer planet," he said. "We hear about sea level rise, but I don't know if people really appreciate the magnitude and the ultimate damage that it will cause economically and politically."

The rift in Larsen C has been there for as long as scientists have been able to observe the shelf, said Daniel McGrath, a glaciologist at Colorado State University. But in the past few years the crack has grown rapidly several times.

Because the Weddell Sea, which lies east of the peninsula, is covered in sea ice, the iceberg might not drift very far. Eventually, ocean and air currents will ferry it along the eastern edge of the peninsula out to the Southern Ocean. But, McGrath said, that could take decades.

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Unlike the collapse of the Larsen A and B ice shelves, which splintered and collapsed over just more than a month after a series of warm summers on the Antarctic Peninsula, the Larsen C shelf hasn't shown the same signs of warming, McGrath said.

The amount of land ice that lies behind Larsen C is relatively small compared to elsewhere on the continent, McGrath said. Lots of ice shelves ring Antarctica and the loss of land ice in other areas is expected to lead to meters of sea level rise.

But, McGrath said, observing changes in Larsen C helps scientists understand ice shelf dynamics, which could help them make meaningful predictions about other shelves, like the Ross ice shelf.

Ross is the largest ice shelf in the Antarctic, covering an area roughly the size of Texas. If it collapsed, huge chunks of West Antarctica would become unstable, White said.

"When that happens, I think we can term that a 'holy shit' moment," he said.

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