An iceberg is a large piece of freshwater ice that has broken off from a snow-formed glacier or ice shelf and is floating in open water.It may subsequently become frozen into pack ice (one form of sea ice). As it drifts into shallower waters, it may come into contact with the seabed, a process referred to as seabed gouging by ice.
Since the density of pure water ice is ca. 920 kg/m³, and that of sea water ca. 1025 kg/m³, typically, only one ninth of the volume of an iceberg is above water. The shape of the remainder under the water can be difficult to surmise from looking at what is visible above the surface. This has led to the expression “tip of the iceberg “, generally applied to a problem or difficulty, meaning that the visible trouble is only a small manifestation of a larger problem.
Though usually confined by winds and currents to move close to the coast, the largest icebergs recorded have been calved, or broken off, from the Ross Ice Shelf of Antarctica. The largest iceberg on record was an Antarctic tabular iceberg of over 31,000 square kilometres 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.
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