An iceberg is a large piece of ice formed from freshwater that has broken off from a glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice. Alternatively, it may come to rest on the seabed in shallower water, causing ice gouging in the land underneath or becoming an ice island. Because the density of pure ice is less than sea water an iceberg will float in sea water with about one-ninth of the volume of an iceberg above water. The shape of the underwater portion can be difficult to judge by looking at the portion above the surface. This has led to the expression "tip of the iceberg", for a problem or difficulty that is only a small manifestation of a larger problem.
Icebergs have always naturally formed. It has been speculated that iceberg formation will increasd as the climate warms. For example, last week, an iceberg four times the size of Manhattan broke off Greenland's Petermann Glacier. The ice island is now drifting south through the Nares Strait between Greenland and Canada. Experts are not sure whether it will make it all the way to the Atlantic and what damage it might cause on its way.
Once icebergs were nameless navigational obstacles such as the one that sunk the Titantic. Nowadays they are named and the larger ones routinely tracked. The following is a list of the more recent large bergs:
* Iceberg B-15 11,000 square kilometres, 2000,
* Iceberg B-15A, 3,100 square kilometres (1,200 sq mi), broke off 2003
* Iceberg C-19, 5,500 km2, 2002
* Iceberg B-9, 5,390 km2, 1987
* Iceberg D-16, 120 sq mi, 2006
The largest is the size of Jamaica and has been floating around Antarctica since its birth slowly melting and crumbling. The letter B indicates its location (Amundsen Sea).
Calving is the process that causes iceberg formation. It can be caused by tidal and seismic events, periodic calving and disintegration of ice masses are considered normal geological processes. One of the most important causal factors in glacial calving is the tendency of the ice to spread out at the terminus of the glacier. Other important variables include tidal fluctuations, storm surges, collisions from other ice masses, melt water wedging into crevasses, and pre-existing flaws along which calving might occur.
Global warming will lead to more melt water that will gradually help widen cracks and break off more icebergs in the future. Presently there is no firm mathematical formula for predicting calving.
Where do the icebergs go? Many stay near where they form. Others drift south or north into more active sea lanes causing potential damage and losses.
For further information: http://en.wikipedia.org/wiki/Iceberg or http://www.npr.org/templates/story/story.php?storyId=129183533&ft=1&f=1025