You might remember from An Inconvenient Truth that back in 2002, over the course of about a month, the Larsen B Ice Shelf of the Antarctic Peninsula disintegrated. It was a section of ice roughly 3,250 square kilometers, or 1,250 square miles, in size. (You can read more about and see the NASA satellite images here http://earthobservatory.nasa.gov/Features/WorldOfChange/larsenb.php )
|February 17, 2002 image of Larsen B ice shelf as it breaks up|
Ice shelves are floating bands of ice that extend out from glaciers that are located on land. Glaciers, by definition, are formed of ice that is flowing from a zone of accumulation to a zone of ablation (loss or removal), so they are constantly in motion. Ice sheets gain mass from ice flowing into them from their on-land glacial sources, from snow accumulation and from ocean water freezing to the underside. They lose mass by calving icebergs (i.e. pieces break off at the outer edge), melting along their outer margins and sublimation (ice going directly into water vapor phase). Usually all of this is a relatively ponderous process - with ice sheets advancing or retreating slowly over time.
A collapse is much more dramatic - occurring over a relatively short period of time as a result of long term environmental changes that thin and shrink the ice. At some point, a tipping point is reached and rather than icebergs breaking off the toe of the ice shelf, the entire shelf fractures and falls to pieces.
It looks like Larsen C is now showing sign of potential collapse. Researchers are reporting that a rift in Larsen C advanced rapidly last year (see the magenta dots on the figure below). Further, they state that this rift "is likely in the near future to generate the largest calving event since the 1980s and result in a new minimum area for the ice shelf." The paper concludes "It seems inevitable that this rift will lead to a major calving event which will remove between 9 and 12 % of the ice shelf area and leave the ice front at its most retreated observed position. More significantly, our model shows that the remaining ice may be unstable. The Larsen C Ice Shelf may be following the example of its previous neighbour, Larsen B, which collapsed in 2002 following similar events."
This might help with orienting yourself ...