Icebergs should be distinguished from polar pack ice, which is frozen sea water, and from ice islands, which are large areas of consolidated multi-year pack ice. An iceberg is a large mass of ice which has broken off and drifted from parent glaciers or ice shelves along polar seas. Icebergs drift with ocean currents into shipping lanes where they constitute a hazard. In polar seas their presence, together with pack ice, may prevent normal shipping movements.
It is estimated that approximately 16,000 icebergs are 'calved' annually in the Northern Hemisphere. Of these, approximately 90% are produced by glaciers along the coast of Greenland. These may weigh over two million tons. About 400 icebergs drift past Newfoundland each year, the remainder having been stranded or eroded in the north. The Northern icebergs are rarely more than 2,000 feet in width or over 400 feet above water level. Antarctic icebergs are much larger and may reach over 100 miles in length. The heaviest concentration of icebergs in the region of the Grand Banks or Trans-Atlantic shipping lanes occurs from April to June each year.
In 2000, a 295 km by 37 km (11,000 sq km) iceberg broke away from the Antarctic's Ross Ice Shelf.