Motion Of Massive Antarctic Ice Berg Causes Another Immense Berg To "Calve"

Satellite images of the new berg indicate dimensions of about 130 kilometers (80 miles) by 20 kilometers (12 miles). The new berg is considerably smaller at 2480 square kilometers (960 square miles) than the piece of ice -- now designated as iceberg B-15 -- which broke off the Ross Ice Shelf earlier in March. Satellite images also indicate that the newest berg appears already to be breaking into several smaller pieces.

B-15 broke off the Ross Ice Shelf roughly 200 miles east of McMurdo Station, the largest of the National Science Foundation's Antarctic Research Stations, and measured about 273 kilometers (170 miles) long by 40 kilometers (25 miles) wide. Its area of approximately 11,007 square kilometers (4,250 square miles) is roughly equivalent to the state of Connecticut's.

NSF-supported researcher Douglas MacAyeal, of the University of Chicago, said that his models of iceberg behavior, based on the calving of previous large icebergs in other areas of Antarctica, led him to conclude correctly that B-15 was likely to collide repeatedly with the Ross Ice Shelf and cause other large bergs to split off.

"The tides are constantly trying to move a new iceberg in a circular orbit," said MacAyeal. "The effect of that motion is that the iceberg that has just calved is like a bull in a china shop and that causes anything else that is ready to calve to come off too."

MacAyeal said that tides and currents around Antarctica aren't well understood, making it difficult to predict the fate of B-15 and the newer berg that it has spawned. But, he added, tidal motion may cause collisions that will calve other large bergs over the next several weeks before these two big icebergs begin to drift away from the Ross Ice Shelf.

"The appearance of this new iceberg confirms this dynamic," he said, "The fact is that we could be in for more calving."

Large icebergs, similar in size to B-15 have calved from the Ross Ice Shelf before, notably in 1956. But MacAyeal noted that today's ability to watch the calving of these icebergs almost as it happens through satellite imagery is very exciting to scientists.

Matthew Lazarra, a researcher at the NSF-funded Antarctic Meteorological Center at the University of Wisconsin, first noticed the calving of the new iceberg while scanning satellite photographs of B-15 and a smaller fragment of that berg, dubbed B-16. Both B-15 and B-16 had been obscured by cloud cover for a period of several hours.

Lazarra said that the latest satellite images indicate that the newest berg already appears to have broken into as many as four smaller pieces.