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Uh oh: The rift that’s about to cleave off a massive Antarctic iceberg has a sibling

Rift in the Larsen C Ice Shelf as seen from a NASA aircraft on Nov. 10, 2016.

Scientists keeping close watch on the Larsen C Ice Shelf in Antarctica have noticed something new: The rift, which has been opening across the shelf for some time, now has a sibling.

Using a highly-sensitive European Space Agency satellite known as Sentinel-1, scientists have been tracking the progress of a lengthening and widening crack across the floating Larsen C Ice Shelf. Once this crack reaches a certain point — exactly when is unclear — it could break off one of the largest icebergs on record.

Recently, though, the main fissure has not progressed further across the ice shelf, since it’s hung up in an area of softer ice known as a "suture zone," slowing its forward speed.

However, while progress of the main rift seems to have slowed, scientists have spotted a "new branch" of the rift heading toward the ice front, where the ice shelf meets the sea.

Larsen C Ice Shelf rift update: No major advance since February, but #Sentinel1 InSAR shows the rift branched in the last 6 days @ESA_EO pic.twitter.com/7rhjcGjnKs

— Adrian Luckman (@adrian_luckman) May 1, 2017

"As of May 1, 2017, we have observed a significant change in the rift on the Larsen C ice shelf," researchers affiliated with the British research project known as "Project MIDAS," wrote on their website.

According to the scientists, eventually the ice shelf rifts will cause the Larsen C Ice Shelf to suddenly lose more than 10 percent of its area, which will leave the front of the ice shelf at a far more vulnerable, retreated position, where it can be more easily undermined through warming ocean waters and increasing air temperatures.

The scientists are using the Sentinel’s synthetic aperture radar to discern the rift’s behavior, since it is currently winter in Antarctica, making visual confirmation difficult to impossible. They’ve noticed that even though the length of the rift has stopped increasing, it has continued to widen at more than 1 meter, or 3.2 feet, per day. The new branch of the ice crack may be helping to accelerate this widening trend.

Eventually, Larsen C may meet the same fate as its neighbor, Larsen B, which broke up suddenly in 2002 after a similar event. (That sudden breakup helped inspire the opening scene in the climate change disaster film, The Day After Tomorrow.)

While any breakup of Larsen C would not cause an immediate increase in global sea levels, since the ice is already floating, thereby displacing water like an ice cube floating in a water glass, it could be a gateway to future trouble.

Such floating ice shelves act as door stops on land-based ice floes, and when they pop out, the inland ice can flow faster into the sea, thereby raising sea level.

This is playing out everywhere from Greenland to West Antarctica, causing scientists to raise their projections for sea level rise through the end of this century. In fact, this is one of the main reasons why researchers are paying so much attention to one rift (well, now two rifts) on a single ice shelf in Antarctica.

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