This Monday, July 16, 2012 NASA image provided by the University of Delaware shows a crack in northwestern Greenland's Petermann Glacier. On Monday, July 16, 2012, an iceberg twice the size of Manhattan tore off one of Greenland's largest glaciers, indicated at center. Scientists had been watching a 15-mile long crack in the floating ice shelf of the glacier for several years. On Monday NASA satellites showed it had broken completely, forming the 46 square mile iceberg. Petermann spawned an iceberg twicethat size in 2010. (AP Photo/NASA, University of Delaware)