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2011-11-03 12:52:38
By OurAmazingPlanet Staff Space.com
A huge, emerging crack has been discovered in one of Antarctica's glaciers,
with a NASA plane mission providing the first-ever detailed airborne
measurements of a major iceberg breakup in progress.
NASA's Operation Ice Bridge, the largest airborne survey of Earth's polar ice
ever flown, is in the midst of its third field campaign from Punta Arenas,
Chile. The six-year mission will yield an unprecedented three-dimensional view
of Arctic and Antarctic ice sheets, ice shelves and sea ice. The glaciers of
the Antarctic, and Greenland, Ice Sheets, commonly birth icebergs that break
off from the main ice streams where they flow in to the sea, a process called
calving.
The crack was found in c, which last calved a significant iceberg in 2001; some
scientists have speculated recently that it was primed to calve again. But
until an Oct. 14 IceBridge flight, no one had seen any evidence of the ice
shelf beginning to break apart. Since then, a more detailed look back at
satellite imagery seems to show the first signs of the crack in early October.
"We are actually now witnessing how it happens and it's very exciting for us,"
said IceBridge project scientist Michael Studinger of NASA's Goddard Space
Flight Center in Greenbelt, Md. "It's part of a natural process, but it s
pretty exciting to be here and actually observe it while it happens."
Gravity pulls the ice in the glacier westward along Antarctica's Hudson
Mountains toward the Amundsen Sea. A floating tongue of ice reaches out 30
miles (48 kilometers) into the Amundsen beyond the grounding line, the
below-sea-level point where the ice shelf locks onto the continental bedrock.
As ice pushes toward the sea from the interior, inevitably the ice shelf will
crack and send a large iceberg free. [Photo Album: Antarctica, Iceberg Maker]
Pine Island Glacier is of particular interest to scientists because it is big
and unstable and so is one of the largest sources of uncertainty in global sea
level rise projections.
A primary goal of Operation IceBridge is to put the same instruments over the
exact same flight lines and satellite tracks, year after year, to gather
meaningful and accurate data of how ice sheets and glaciers are changing over
time. But discovering a developing rift in one of the most significant science
targets in the world of glaciology offered a brief change in agenda for the
Oct. 26 flight, if only for a 30-minute diversion from the day's prescribed
flight lines.
The IceBridge team observed the rift running across the ice shelf for about 18
miles (29 km), using an instrument called the Airborne Topographic Mapper,
which uses a technology called lidar (light detection and ranging) that sends
out a laser beam that bounces off a surface and back to the device. The lidar
instrument measured the rift's shoulders about 820 feet (250 meters) apart at
its widest, although the rift stretched about 260 feet (79 meters) wide along
most of the crack. The deepest points from the ice shelf surface ranged from
165 to 195 feet (50 to 60 meters).
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 the shelf 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.