Icebergs

Icebergs (from ice and berg, mountain, mountains of ice) form in two conditions:

  • when a glacier descends to the sea or to a lake, the terminal part of the snout starts floating when it comes into contact with water. Because of a phenomenon known as calving, large fractures form in the mass of ice, with the consequent detachment of portions of different sizes. The shape of this kind of iceberg is generally irregular, and the surface is jagged, tormented;
  • the movements of currents and tides of the underlying water, together with the constant thrust of the glaciers that feed the ice shelves, cause fractures and fragmentation of the ice shelves. Every year, in Antarctica, for example, 1,450 to 2,000 km3 of ice are lost in this way (a volume that is equivalent to about half the annual amount of drinking water consumption worldwide).

These kinds of icebergs generally have the shape of flat tablelands whose surface is relatively smooth and regular. These are typical in the Antarctic zone, while icebergs of the first type form more easily in the Arctic seas, where lands are not surrounded by ice shelves of floating ice and the numerous glaciers from the land can therefore flow directly into the sea. Small sized icebergs may also form from blocks of ice collapsing from the fronts, which do not necessarily have to be floating on the sea or on a lake.
Since the density of ice is less than the density of water, icebergs float on the surface of the sea; the submerged part is therefore 7-10 times (depending on the difference in density of water and ice) taller than the part above sea level. If we consider that some icebergs can be many dozens of metres high, above the surface of the sea, then we can well understand how the name “mountains of ice” is particularly indicated : for example, an iceberg that shows a 30 metre wall continues below sea level up to a depth of over 200 metres! The largest iceberg to be seen was an iceberg in the Antarctic, observed in 1956, whose size was 335 x 97 km, with a surface area of 31,000 km2, equal to the area of Belgium.
Once they detach from the glacier or the ice-shelf, icebergs begin to drift pushed by winds, currents and tides. The erosion of wind and waves and the progressive melting process they undergo as they move towards warmer latitudes, decrease their size, besides the fragmentation caused by violent tempests or collisions with other icebergs or with the land. The destiny of icebergs, therefore, is to decrease in size till they disappear, however their life-span can be of many years.

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