In early 2000, an iceberg covering more than 4,000 square miles broke off from Antarctica's Ross Ice Shelf. Scientists first observed signs of the iceberg calving, or breaking away, on March 17, 2000. Measuring about 183 by 22 miles, it may be the biggest iceberg on record.
Known as B15, this huge iceberg was nearly the size of Connecticut. It was trailed by a small "companion iceberg" called B16. Another significant iceberg calved around March 31, 2001. Known as—guess what?—B17, it was about 80 by 12 miles, or roughly the size of Rhode Island. Icebergs of this size calve from the ice sheets of Antarctica about every other year.
More than 90 percent of Antarctica is composed of massive sheets of ice, which in some places are thousands of feet thick. The continent is about the size of the United States. Although it has been slowly melting since the end of the last ice age, it is possible that global warming is now speeding up the process. Because of this melting and the calving of icebergs, the boundaries of Antarctica shift slightly with each passing year.
The Ross Ice Shelf, source of the new icebergs, is a Texas-sized slab of floating ice that borders the Pacific Ocean. Ice shelves occur when some of the ice covering Antarctica gradually slips off and floats on the sea, remaining attached like a shelf to the continent. Cracks in the ice shelves are constantly forming as a result of tides and storms. Over the years, these cracks may let huge chunks of ice break free.
Most Antarctic icebergs stay close to home, trapped in the strong currents surrounding the continent. For example, a Rhode Island–sized iceberg known as B9 calved in 1989 and is still wandering near its icy home. Some icebergs have drifted all the way around Antarctica twice before entering the Atlantic Convergence Zone north of the continent. There, warmer waters melt the icebergs from beneath, soon dissolving them entirely.
But not all bergs are homebodies. Seven years ago, iceberg B10A drifted away from Antarctica. This iceberg became a danger to shipping lanes not just because of its great size—about 1,000 square miles—but because it left a deadly trail of thousands of small icebergs. One scientist described these baby bergs as ranging "in size from as big as a house to as big as a grand piano." B10A was observed wandering off the tip of South America before meeting warmer waters and dissolving in February 2000.
It is rare for Antarctic icebergs to endanger ships the way icebergs further north can. Every year, thousand of icebergs in the North Atlantic calve from Greenland and drift toward the shipping lanes that run between Europe and North America. After one such iceberg famously sunk the Titanic in 1912, the International Ice Patrol was formed to help protect ships in the North Atlantic. It uses satellite technology to patrol the North Atlantic during "iceberg season," which lasts from February to October.