Update: 12 p.m. Jan. 6, 2017
A huge area of the Larsen C ice shelf is close to collapsing, the British Antarctic Survey reported Friday. A team of glaciologists has been using seismic equipment to study the seafloor beneath, but because satellite observations show a break up is likely, the team will now study the area by air.
"Because of the uncertainty surrounding the stability of the Larsen C ice shelf, we chose not to camp on the ice this season. Researchers can now only do day trips from our Rothera Research Station with an aircraft nearby on standby," said David Vaughan, director of science at British Antarctic Survey, in a statement.
A dramatic NASA photograph (above) taken in November revealed a huge scar in the ice shelf, a fissure that is threatening to split the shelf in two and calve off an iceberg the size of Delaware. The photograph, taken by scientists on NASA's IceBridge Mission, shows a crack in the ice shelf, on the eastern coast of the northern Antarctic Peninsula, that is approximately 70 miles long, 300 feet wide, and about one third of a mile deep.
The fissure cuts all the way through to the bottom of the ice shelf, but does not yet reach fully across it.
Daniel McGrath, a glaciologist at Colorado State University, said he and other scientists have been tracking the rift particular interest since 2014, when satellite imagery showed that it was undergoing rapid growth.
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"This rift is part of a whole series," McGrath said, "which have been stalled in the same spot since at least the mid-1960s, according to some of the earliest aerial photographs of the ice shelf. Back around 2005, one of these rifts developed a sub-rift that split off from its side and grew about 10 kilometers [6 miles] from 2005 to about 2008, and then was largely stationary until 2014, at which point it began undergoing fairly dramatic growth."
The presence of rifts in an ice shelf is not by itself inherently unusual. They are in fact a natural and expected feature in such a dynamic environment. "What is concerning is when rifts develop and propagate in regions where we have not seen them previously," he saud, which is the situation with this latest fissure.
It's uncertain what will happen to the rest of Larsen C when the calving occurs, and whether the event will make the shelf inherently less stable. The smaller Larsen A shelf collapsed in 1995, and Larsen B - larger than A, but still much smaller than C, and situated between the two - largely broke apart into a myriad small pieces in 2002. So is the rift in Larsen C merely the latest, inevitable sign of disintegrating ice in a part of the Antarctic that has experienced considerable warming?
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"Yes and no," McGrath said. "Yes, in the sense that we've seen some dramatic warming on the Peninsula in the last half century, and as it's progressively warmed, the line of stability of ice shelves has essentially marched down the Peninsula. So that would theoretically put Larsen C at risk. Before this rift propagated, the previous concern for Larsen C was the thinning of the ice shelf. Out near the ice front, where the ice shelf meets the ocean, there are two ice rises - basically, rock protrusions on which the ice is sitting. And so the concern was that if the ice shelf continued to thin over the next 100 or so years, it would lose contact with those ice rises and that would make it inherently unstable, because all of a sudden you've lost this resistance. That was the primary concern. But now that we have this rift spreading across it, it's opened a whole new can of worms in terms of its stability.
"The disintegration of Larsen B was really a climatic warming signal. Increased surface melt over many years, which eventually propagated through the ice shelf, led to its disintegration. Larsen C is not preconditioned to suffer a similar collapse at present. But this new fracture certainly threatens its stability, and raises important questions of how the shelf will respond."
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