Iceberg

An iceberg is a large piece of freshwater ice that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Small bits of disintegrating icebergs are called 'growlers' or 'bergy bits'. An iceberg is a large piece of freshwater ice that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Small bits of disintegrating icebergs are called 'growlers' or 'bergy bits'. Up to 90 percent of an iceberg is below the surface. The expression 'tip of the iceberg', illustrates a small part of a larger unseen issue. Icebergs are considered a serious maritime hazard. The 1912 loss of the 'unsinkable' RMS Titanic led to the formation of the International Ice Patrol in 1914. Icebergs calved by glaciers that face the open sea, such as in Greenland, are irregular shaped piles. In Antarctica, ice shelves calve large tabular (table top) icebergs. The biggest iceberg ever recorded was Iceberg B-15A which split off the Ross Ice Shelf in Antarctica in 2000. The word iceberg is a partial loan translation from the Dutch word ijsberg, literally meaning ice mountain, cognate to Danish isbjerg, German Eisberg, Low Saxon Iesbarg and Swedish isberg. Because the density of pure ice is about 920 kg/m3, and that of seawater about 1025 kg/m3, typically about one-tenth of the volume of an iceberg is above water (which follows from Archimedes's Principle of buoyancy). The shape of the underwater portion can be difficult to judge by looking at the portion above the surface. The visible 'tips' of icebergs typically range from 1 to 75 metres (3 to 200 ft) above sea level and weigh 100,000 to 200,000 metric tons (110,000 to 220,000 short tons). The largest known iceberg in the North Atlantic was 168 metres (551 ft) above sea level, reported by the USCG icebreaker East Wind in 1958, making it the height of a 55-story building. These icebergs originate from the glaciers of western Greenland and may have interior temperatures of −15 to −20 °C (5 to −4 °F). Winds and currents tend to move icebergs close to coastlines, where they can become frozen into pack ice (one form of sea ice), or drift into shallow waters, where they can come into contact with the seabed, a phenomenon called seabed gouging. The largest icebergs recorded have been calved, or broken off, from the Ross Ice Shelf of Antarctica. Iceberg B-15, photographed by satellite in 2000, measured 295 by 37 kilometres (183 by 23 mi), with a surface area of 11,000 square kilometres (4,200 sq mi). The largest iceberg on record was an Antarctic tabular iceberg of over 31,000 square kilometres (12,000 sq mi) sighted 150 miles (240 km) west of Scott Island, in the South Pacific Ocean, by the USS Glacier on November 12, 1956. This iceberg was larger than Belgium. A small iceberg less than 2 meters (6.6 feet) across that floats with less than 1 meter (3.3 feet) showing above water is called a growler, and is smaller than a bergy bit, which is usually less than 5 meters (15 feet) in size. Both are generally spawned from disintegrating icebergs.