A Runaway Iceberg

Researchers are monitoring an enormous iceberg that broke off the Ross Shelf in Antarctica last March in an effort to understand the nature of future breakaway 'bergs.

The fragment, called B-15-A, stands approximately 15 stories above the water and is 90 miles long and almost 30 miles wide.

Towers have been erected on the iceberg with sensors to monitor its movement and the weather.

Hourly updates are sent by satellite to researchers at the University of Chicago, which tracks the iceberg to understand and predict the paths of future icebergs.

B-15-A is part of one of the largest icebergs ever recorded to have broken away from Antarctica's Ross Ice Shelf. The original iceberg, called B-15, was 180 miles long, but has since broken into two large pieces, B-15-A and B-15-B.

Currently, B-15-A is drifting toward McMurdo Sound. The National Science Foundation's McMurdo Station, the largest scientific research station on the continent, is located on Ross Island in the sound.

The project is funded by the National Science Foundation, with the assistance of the U.S. Coast Guard icebreaker Polar Sea.

Scientists have worried for decades that the Antarctic ice sheet was shrinking, threatening a global rise in sea level. That's why they are monitoring the ice closely, looking for signs of whether the ice is melting faster because of global warming.

Melting doesn't mean that it is time to get into boats, say researchers, but local wildlife is already affected. CBS News Correspondent Jerry Bowen reports the iceberg has sealed off the Cape Crozier penguin colony on Antarctica, home to a half million Adelie penguins. If the iceberg doesn't move on, several generations of penguins could be affected as they try to migrate to and from the cape.

So overall, the iceberg may well be a "yellow warning flag" that confirms long-term changes are under way in the ice fields covering the South Polar region.

Along those lines, another science group reported recently that satellite studies show that about 7.5 cubic miles of ice have eroded from a key area of Antarctica in just eight years.

The study, which appears in the journal Science, involved altitude measurements of the West Antarctica Ice Sheet, the smaller of two major ice sheets. It covers 740,000 square miles of the frozen continent.

Based on satellite measurements, said Andrew Shepherd, a University College London geologist and an author of the study, it appears that since 1992 the ice sheet has lost ice principally through the speeded-up movement of the Pine Island Glacier, an ice stream that drains about a third of the ice sheet.

"The Pine Island Glacier is key," said Shepherd. "It is totally exposed to the sea, and people have identified it as the weak underbelly of the West Antarctica Ice Sheet."

Melting of the entire sheet theoretically could cause a global sea levl rise of 25 to 45 feet, but Shepherd said that at the present rate of change it would take centuries for the Pine Island Glacier, which is only about 10 percent of the ice sheet, to affect sea level seriously.