Iceberg is Calved in Antarctica

Scientists at British Antarctica Survey (BAS) using Polar View program data from the European Space Agency's (ESA's) Envistat satellite sighted an iceberg the size of central London that had broken off from the Pine Island Glacier on the edge of the Western Antarctic Ice Sheet (WAIS).

Ice sheets cover whole continents with ice fields. Antarctica and Greenland alone of all the continents have ice sheets. Glaciers form on ice sheets or, alternately, in mountains and are essentially rivers of ice that respond to gravity and carry melted ice from the interior of the ice sheet and collect it at the sea's edge.

As a natural part of the cycle of seasons in an ice sheet ecosystem, icebergs regularly break away from the glaciers. After 34 years of collected data, scientists can say that an exceptionally large iceberg breaks away from a glacier every 5 to 10 years, with the most recent prior break-away of a large iceberg occurring in 2001.

When icebergs break away in this fashion, they do not raise sea level because they are already floating. Tongues of ice from glaciers project out away from the bedrock, which is many hundreds of meters below the ice sheet and glacier, into the sea waters. This projection of ice is what gives rise to icebergs, so the ice making up icebergs is already floating.

Pine Island Glacier in Western Antarctica has the attention of scientists all over the world because it is the largest glacier on the WAIS and the rate at which it is flowing has undergone a continual increase during the last 15 years. This has resulted in the location at which the glacier projection meets the sea has retreated further back. This is true even though satellite data from 1973 onwards indicates that the glacier tongue has fluctuated more or less around this locale since 1973. Further, when the last large iceberg broke off from Pine Island Glacier in 2001, the glacier tongue measured at a record level of retreat. After that, the tongue regained some ground, but with this new iceberg break, the Pine Island Glacier tongue has once again retreated to its prior 2001 position.

Icebergs breaking away from a main glacier are said to be "calving." Satellite data shows that calving is a natural result of the effects of wind and waves. Calving also occurs when glacier tongue projections get to be too large to be supported by the surrounding waters. Additionally, previously formed icebergs that are still in the area can hit the glacier tongue and break new icebergs off from the glacier.

An animation created from the ESA's Envistat satellite Polar View program data is available on the ESA Web site where this calving event is also discussed.

"Giant iceberg breaks off from Antarctic glacier," British Antarctic Survey.

"Earth from Space: Birth of an iceberg," European Space Agency.