Wednesday, December 14, 2016

Close look at a crack on Larsen C

acquired November 10, 2016

From NASA 

In late August 2016, sunlight returned to the Antarctic Peninsula and unveiled a rift across the Larsen C Ice Shelf that had grown longer and deeper over the austral winter.
Satellites spotted it in natural-color imagery.

 Larsen Ice Shelf in the GeoGarage platform (NGA chart)

By November, the arrival of longer days and favorable weather made it possible for scientists to take a closer look.

 acquired November 10, 2016

These photographs show close and wide views of the rift from the vantage point of NASA’s DC-8 research aircraft.
NASA scientist John Sonntag snapped the photos on November 10, 2016, during an Operation IceBridge flight.
The mission, which makes airborne surveys of changes in polar ice, completed its eighth consecutive Antarctic deployment later that month.

 A NASA study says that Antarctica's Larsen Ice Shelf
is likely to disintegrate before the end of this decade.

The rift in Larsen C measures about 100 meters (300 feet) wide and cuts about half a kilometer (one-third of a mile) deep—completely through to the bottom of the ice shelf.
While the rift is long and growing longer, it does not yet reach across the entire shelf.
When that happens, Larsen C will shed an iceberg about the size of Delaware.

 Operation IceBridge, a NASA airborne survey of changes in polar ice, recently completed its eighth consecutive Antarctic deployment.
This page contains a wrapup video for the entire mission, as well as some footage over the Antarctic Peninsula's Larsen C Ice Shelf, and a few high definition still images.
One of this year’s missions flew over a massive rift in the Larsen C.
Ice shelves are the floating parts of ice streams and glaciers, and they buttress the grounded ice behind them; when ice shelves collapse, the ice behind accelerates toward the ocean, where it then adds to sea level rise.
Larsen C neighbors a smaller ice shelf that disintegrated in 2002 after developing a rift similar to the one now growing in Larsen C.
The IceBridge scientists measured the Larsen C fracture to be about 70 miles long, more than 300 feet wide and about a third of a mile deep.
The crack completely cuts through the ice shelf but it does not go all the way across it – once it does, it will produce an iceberg roughly the size of the state of Delaware.

Cracks and calving of ice from the front of an ice shelf are normal.
Shelves are fed by glaciers and ice streams coming from the interior of the continent.
They advance into the ocean until a calving event takes place.
The shelf front retreats and then advances again.
The whole cycle can occur over the span of a few decades.
But calving that happens faster than a shelf can re-advance can mean trouble for an ice shelf.
For example, large and frequent calving events at Larsen B preceded that shelf’s final period of rapid disintegration, which occurred in just six weeks in 2002.
Whether Larsen C will respond in a similar way remains to be seen, but that’s one reason why scientists plan to make observations before and after the next calving event.

Ice shelves float, so they do not directly contribute to sea level rise.
They are important, however, because they buttress land ice and keep it inland.
If a shelf disintegrates, glaciers that feed it can flow more quickly out to sea—a process that directly increases sea level.

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