A giant sheet of ice measuring 260 square kilometre has broken off a glacier in Greenland. According to researchers at a US university, the block of ice separated from the Petermann Glacier, on the north-west coast of Greenland. It is the largest Arctic iceberg to calve since 1962, said Prof Andreas Muenchow of the University of Delaware.The ice could become frozen in place over winter or escape into the waters between Greenland and Canada. He said it was not clear if the event was due to global warming. Thousands of icebergs calve off Greenland's glaciers annually, but they are seldom so large.