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Earth from Orbit: World’s Largest Iceberg Begins to Break Up

May 28, 2021

An iceberg nearly the size of Delaware sheared off from the edge of Antarctica earlier this month and floated into the Weddell Sea, where it is now starting to fracture into pieces. The iceberg, named A-76 by the U.S. National Ice Center, measured 1,668 square miles before breaking up. 

The Joint Polar Satellite System’s polar-orbiting satellites observed A-76 splitting from the Ronne Ice Shelf on May 15 and May 16 during multiple flyovers.

The VIIRS instrument on these satellites can see ice sheets, ice shelves and icebergs, such as A-76, at a high spatial resolution of 375 meters, and the instrument's wide swath and frequent overpasses at the poles resulted in good coverage of this calving event. 

VIIRS is used extensively for cryosphere work, said Dr. Jeff Key, branch chief of advanced satellite products at NESDIS and lead of the cryosphere teams for the JPSS and GOES-R programs at NOAA’s Cooperative Institute for Meteorological Satellite Studies, or CIMSS. VIIRS also plays an important role in mapping and monitoring glaciers, along with measuring the surface albedo and temperature of ice sheets and the ice concentration, thickness, surface temperature and motion of sea ice.

Because A-76 is floating ice, it won’t raise the sea level, Key said.  

“It’s like ice cubes in your drink,” Key said. “When they melt, they don’t cause the glass to overflow.

This calving event is a result of the natural hydrological cycle, he said. Over time, warm water melts the underside of the ice shelf, causing it to deteriorate. Meanwhile, meltwater on the surface percolates through cracks, further eroding the shelf. 

Also, this particular iceberg came from the very western flank of the ice shelf, according to Dr. Kelly Brunt of the Cryospheric Sciences Laboratory at NASA’s Goddard Space Flight Center

“Along the flanks, there are a lot more “rift precursors” or fractures in the ice, due to the proximity to the shear margins,” she said. Those fractures could easily lead to more breakup.” 

Dr. Key and William Straka III wrote this article on another iceberg, A-68, which broke from the Larsen C Ice Shelf in 2017. The largest iceberg on record is B-15, which measured 4,200 square miles. B15 calved from Antarctica’s Ross Ice Shelf in March 2000, eventually fracturing into smaller pieces. 

The NOAA-20 and Suomi-NPP satellites orbit the Earth from pole to pole at an altitude of 512 miles, providing high-resolution imagery and taking temperature and moisture measurements throughout the atmosphere.