BioEd Online

The plodding course of the Long Island-sized iceberg, which scientists predicted would crash into an Antarctic glacier by 15 January, has been halted indefinitely.

The iceberg, called B-15A, has run aground about four kilometres from the Drygalski Ice Tongue and is "just jiggling back and forth", says Julie Palais, a glaciologist who works at McMurdo Station, a US Antarctic research base. It will probably stay like this for some time, she adds.

Some scientists are concerned that B-15A will inhibit the movement of ships in McMurdo Sound, and force penguins to travel farther for food. But Palais says that there is no reason for concern.

"B-15A is nowhere near the penguin colonies that are being studied by our researchers," she says. "Ships are not currently being affected, and we have no reason to think that this will change."

In March 2000, the longest iceberg ever seen broke off the Ross Ice Shelf, a floating mass of ice east of McMurdo Station. In a few weeks the iceberg, named B-15, split into several pieces, the largest of these being B-15A.

As snow accumulates on the mainland, it compacts and forms ice. As ice builds up, it flows outward into floating shelves and is sloughed off the front of these as an iceberg. The rate of iceberg formation depends on how much snow falls, says Neal Young of the Antarctic Cooperative Research Center at the University of Tasmania, Australia.

Global warming has increased the number of icebergs breaking away from the Antarctic mainland, but B-15's calving is still thought to be a natural occurrence, says Young.