A very large Antarctic iceberg bigger than the island of Guam, half the size of Greater London, and roughly six times as big as Manhattan is headed for the open ocean. It is 33 km long, 20 km wide, and up to 500 metres thick. The iceberg, named B31, broke off the Pine Island Glacier last November and researchers have been watching it ever since. The glacial crack that created the iceberg was first detected in 2011. The iceberg has floated across Pine Island Bay, a basin of the Amundsen Sea.