Photo Credit: German Aerospace Center (DLR)

A German satellite captures an image on July 8 of an iceberg forming to the left of Pine Island Glacier Ice Shelf. While the calving event is considered a natural phenomenon, the glacier upstream that feeds into the ice shelf is one of the fastest moving in Antarctica, contributing to sea-level rise.

Breaking away

Giant iceberg calves from Pine Island Glacier Ice Shelf

Nearly two years after NASA scientists discovered a huge crack across the Pine Island Glacier (PIG) Ice Shelf, an iceberg bigger than the city of Chicago calved off into the Amundsen Sea.

Scientists at the Alfred Wegener Institute-Helmholtz Centre for Polar and Marine Research broke the news this week. They had been studying the ice shelf from space using a German satellite called TerraSAR-X . [View a time-lapse video of the calving iceberg.]

The iceberg measures about 720 square kilometers (Chicago is about 600 square kilometers). Scientists at the Polar Geospatial Center (PGC) at the University of Minnesota posted on their Facebook page this week that there is still a small remnant of the iceberg clinging to the rest of the ice shelf.

Pine Island Glacier (PIG) is the fastest flowing glacier in Antarctica, moving about 4,200 meters per year where it feeds into the ice shelf, which floats on the ocean. While PIG has been the focus of climate change studies in recent years, the calving of the ice shelf is believed to be a natural phenomenon.

The crack was first seen and photographed on Oct. 14, 2011, by scientists aboard NASA’s DC-8 — a flying laboratory that boasts a suite of radars and other instruments —as part of Operation IceBridge . [See previous article — Cracked: Rift spotted in Pine Island Glacier Ice Shelf before upcoming expedition.]

The six-year airborne campaign has conducted measurements of ice in the Arctic and Antarctic since 2009 after the Ice, Cloud, and land Elevation Satellite (ICESat) was decommissioned that same year. NASA plans to launch ICESat-2 by 2016 to continue space-based monitoring of the polar regions.

The IceBridge project has been based out of Punta Arenas, Chile, during its previous field seasons. This year NASA plans to base the mission out of McMurdo Station , the hub of the U.S. Antarctic Program , which is managed by the National Science Foundation .

During the 2012-13 season, U.S. and British scientists collaborated on a logistically intensive field project called PIG (for PIne Island Glacier) to study the ice shelf. A team drilled through the 500-meter-thick ice shelf in three locations to deploy instruments below the ice shelf to learn about how the ocean below is melting the underside. [See previous article — Antarctica's ground zero: Expedition heads to Pine Island Glacier region to study thinning ice shelf — and NSF press release .

The field work took place more than 15 kilometers south of the crack where the iceberg broke away from the ice shelf.

The thinning ice shelf allows the glacier behind it to flow faster. PIG, along with nearby Thwaites Glacier, are draining the most ice from the West Antarctic Ice Shelf. The entire ice shelf holds enough frozen water to raise sea level by an estimated five meters. The much larger and higher — and more stable — East Antarctic Ice Shelf would raise sea level by about 60 meters.