Iceberg Antarctica: Iceberg, the Size of Chicago, Breaks off Pine Island Glacier

An iceberg in Antarctica broke off and is now floating freely around the Amundsen Sea. The iceberg, which broke off Antarctica's Pine Island Glacier on Monday, is larger than the entire city of Chicago.

The new iceberg is roughly 278 square miles (720 square kilometers) big. It was seen by an earth-observing satellite called TerraSAR-X, which is operated by the German Space Agency (DLR), LiveScience reports.

There were signs that the iceberg was going to fall off as scientists with NASA's Operation IceBridgefirst first noticed a giant crack in the glacier in October 2011 as they did a fly over. At that time, they noticed a crack about 15 miles in length and 164 feet in width, the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany noted. By May 2012, researchers saw a second crack on the northern side of the first crack by looking at satellite images.

"As a result of these cracks, one giant iceberg broke away from the glacier tongue," Angelika Humbert, a glaciologist at the Alfred Wegener Institute, said in a statement according to LiveScience.

Humbert and her coworkers had studied satellite images of the glacier to track the cracks.

"Using the images we have been able to follow how the larger crack on the Pine Island Glacier extended initially to a length of 28 kilometers [17 miles]," Nina Wilkens, one of the team researchers from the Alfred Wegener Institute, said. "Shortly before the 'birth' of the iceberg, the gap then widened bit by bit so that it measured around 540 meters [1,770 feet] at its widest point."

The Pine Island Glacier often drops icebergs as it flows out to sea. There is still a mystery behind the way icebergs break off though.

"Glaciers are constantly in motion," Humbert said. "They have their very own flow dynamics. Their ice is exposed to permanent tensions and the calving of icebergs is still largely unresearched."

The last time the Pine Island Glacier produced large icebergs was in 2001 and 2007. It is the longest and fastest-changing glacier on the West Antarctic Ice Sheet. Some scientists are trying to determine if global warming is causing the ice sheets to get thinner.