A 40-mile-wide iceberg in Antarctica, the largest in the world and weighing a whopping 1 trillion tons, is on the move after decades grounded to the sea floor, the British Antarctic Survey (BAS) announced.Known as the A23a iceberg, the ice mass had been grounded on the sea floor since shortly after it calved from the Filchner Ice Shelf in August 1986, BAS said. Its size is equivalent to the Hawaiian island of Oahu and three times the size of New York City.Footage taken by BAS shows the vast expanse of the iceberg, as seen from the UK’s polar ship, RSS Sir David Attenborough. Attenborough encountered the iceberg about 56 mi (90km) northeast of Joinville Island on December 1. Credit: British Antarctic Survey via Storyful