A New York-sized glacier is about to break off from Pine Island, a huge 30-mile 'tongue' of ice snaking out from the Hudson Mountains to the Amundsen Sea.
After an eighteen-mile long crack in the ice was photographed by NASA's Operation Ice Bridge last month, the scientists have flown a follow-up mission over the 'calving' iceberg.
'We are actually now witnessing how it happens and it’s very exciting for us,' said Ice Bridge project scientist Michael Studinger, Goddard Space Flight Center, Greenbelt, Md. 'To my knowledge, no one has flown a 3D laser imaging instrument over an actively developing rift such as this.'
Pine Island Glacier last calved a significant iceberg in 2001, and some scientists have speculated recently that it was primed to calve again.
But until an Oct. 14 IceBridge flight of NASA's DC-8, no one had seen any evidence of the ice shelf beginning to break apart. Satellite imagery seems to show the first signs of the crack in early October.
Pine Island has scientists' attention because it is both big and unstable – scientists call it the largest source of uncertainty in global sea level rise projections. But the calving underway is part of a natural process, NASA says.
The team diverted their DC-8 back over the glacier for a return scanning mission.
The IceBridge team observed the rift running across the ice shelf for about 18 miles. The Airborne Topographic Mapper makes its precision topography maps with a laser than scans 360 degrees 20 times per second, while firing 3,000 laser pulses per second.
When flying at an altitude of 3,000 feet, as during this flight, it measures a swath of the surface about 1,500 feet wide. The rift is 250 feet wide along most of its length - so the veteran DC-8 pilot had a tricky job to keep the plane straight along the rift. In places, the rift is already 800 feet wide. When the iceberg breaks free it will cover about 340 square miles (880 square kilometers) of surface area.
Radar measurements suggested the ice shelf in the region of the rift is about 1,640 feet (500 meters) feet thick, with only about 160 feet of that floating above water and the rest submerged. It is likely that once the iceberg floats away, the leading edge of the ice shelf will have receded farther than at any time since its location was first recorded in the 1940s.
'A lot of times when you’re in science, you don’t get a chance to catch the big stories as they happen because you’re not there at the right place at the right time,' said John Sonntag, Instrument Team Lead for Operation IceBridge, based at Goddard Space Flight Center. 'But this time we were.'
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