NASA Operation IceBridge Discovered Major Crack in Pine Island Glacier

In October 2011 NASA’s Operation IceBridge discovered a major crack in the Pine Island Glacier in western Antarctica. 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. Until an October 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. 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. 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), with only about 160 feet of the shelf floating above water and the rest submerged.
source:www.space.com