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Icebergs

Icebergs are chunks of ice that have broken from an ice cap on land and they therefore contain no salt. In the north Polar Regions, glaciers flow down to the sea from the ice caps. When a glacier reaches the water, the front slides in and breaks into large pieces of ice - a process which is called calving. The icebergs then float in the sea and are carried away from the land by currents, or they remain frozen in the pack ice for a year or so. Arctic icebergs drift southwards along the western side of the North Atlantic Ocean and travel as far south as Newfoundland before melting completely. Once in the open ocean they last for less than three months, but they can become a hazard to shipping because of their size. Antarctic bergs differ from those of the Arctic in that they are formed from the ice shelf that surrounds Antarctica. Every year the shelf moves northwards about 100m and during this movement ice breaks off. The bergs may drift as far north as latitude 40°S before melting. Arctic bergs may reach up to 100m out of the water and extend to depths of 400m below the surface, whereas the longer, tabular Antarctic bergs rise to only about 50m above the water and reach only 150m below it, but they can be as large as 330km long and 100km wide. Several thousand icebergs break off from Greenland and Antarctica each year - Greenland alone is the source of about 12,000 a year. Icebergs have caused ships to sink, the best known example being the Titanic which sank in 1912 after hitting a relatively small iceberg. In North Atlantic shipping lanes icebergs are now tracked by the International Ice Patrol, which has been in operation since 1914 in response to the Titanic disaster and now used airborne patrols to spot icebergs. Icebergs do not show up well on radar, but they drift quite slowly and if the location of one is known, ships can alter course around it. Icebergs are an even greater danger to oil rigs at sea. Oil rigs cannot be moved, but could be severely damaged or destroyed if an iceberg drifted into one. Icebergs have been towed away from rigs to prevent col­lisions, but this is often a difficult operation because of the size of the icebergs. Icebergs could, however, be put to use. They are composed of fresh water, and so they would be a useful source of water if it were possible to tow them to arid areas of the world (such as the Middle East) without melting. Unfortunately they can be towed only very slowly and it takes several months to reach a dry area - during which time much of the ice would melt.