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The calving front of Petermann Glacier in northern Greenland as seen from a NASA P-3B. In July 2012 an iceberg twice the size of Manhattan broke off of Petermann Glacier and began to float away in the ocean. After this calving event the line where the iceberg broke away became the glacier's new front edge, or calving front, effectively moving it several kilometers upstream. Credit: NASA/Michael Studinger.