Meltwater Turns Iceberg A-23A Blue

December 26, 2025

The year that iceberg A-23A first broke away from Antarctica’s Filchner Ice Shelf, Ronald Reagan was president of the United States, and the movie Top Gun was setting box office records. Forty years later, the massive tabular berg—one of the largest and longest-lived bergs ever tracked by scientists—is sopping with blue meltwater and on the verge of complete disintegration as it drifts in the South Atlantic between the eastern tip of South America and South Georgia island.

When it first detached from Antarctica in 1986, the berg was nearly twice the size of Rhode Island—about 4,000 square kilometers. Estimates from the U.S. National Ice Center put the berg’s area at 1,182 square kilometers (456 square miles) in early January 2026, following the breakup of several sizable pieces in July, August, and September of 2025 as it moved into relatively warm summer conditions by December.

When the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA’s Terra satellite captured this image of what remained of the waterlogged berg on December 26, 2025, extensive pools of blue meltwater were visible on its surface. Though much smaller than it once was, what remains is still among the largest icebergs in the ocean, covering an area larger than New York City. An astronaut aboard the International Space Station captured a photograph showing a closer view (below) of the iceberg a day later, with an even more extensive melt pool.

The “blue-mush” areas are likely the result of ongoing disintegration events, explained Ted Scambos, a senior research scientist at the University of Colorado Boulder. “You have the weight of the water sitting inside cracks in the ice and forcing them open,” he said. Note also the thin white line around the outer edge of the iceberg seemingly holding in blue meltwater—a “rampart-moat” pattern caused by an upward bending of the iceberg plate as its edges melt at the waterline.

December 27, 2025

The striking linear patterns of blue and white across the berg are likely related to striations that were scoured hundreds of years ago when the ice was part of a glacier dragging across Antarctic bedrock.

“The striations formed parallel to the direction of flow, which ultimately created subtle ridges and valleys on the top of the iceberg that now direct the flow of meltwater,” explained Walt Meier, a senior research scientist at the National Snow & Ice Data Center. “It’s impressive that these striations still show up after so much time has passed, massive amounts of snow have fallen, and a great deal of melting has occurred from below,” added retired University of Maryland Baltimore County scientist Chris Shuman.

The MODIS image suggests that the ailing iceberg has also sprung a leak. The white area to its left may be the result of what Shuman described as a “blowout.” The weight of the water pooling at the top of the towering iceberg would have created enough pressure at the edges to punch through. The blowout may have allowed meltwater to spill tens of meters down to the ocean surface in what researchers call a “freshwater discharge plume,” where it mixed with the mélange of ice bits floating next to the iceberg.

Scientists say these signs indicate the iceberg could be just days or weeks from disintegrating completely. “I certainly don’t expect A-23A to last through the austral summer,” said Shuman, noting that the season typically brings clearer skies and warmer air and water temperatures—factors that accelerate the disintegration process in an area known among ice experts as a “graveyard” for icebergs. It’s already in water that’s about 3 degrees Celsius and riding currents that are pushing it toward even warmer waters that will eat away at it quickly, added Meier.

Even by Antarctic standards, A-23A has had a long, winding journey full of unexpected chapters that have improved scientists’ understanding of the “megabergs” occasionally released into the Southern Ocean. After grounding in the shallow waters of the Weddell Sea for more than 30 years, A-23A broke free in 2020, then spent several months in a twirling ocean vortex called a Taylor column. It eventually spun away and headed north, nearly colliding with South Georgia island and lodging in shallow waters for several months before escaping into the open ocean, where it has been rapidly breaking apart throughout 2025.

Scientists who have been tracking the berg for their entire careers see its imminent demise as a bittersweet moment. “I’m incredibly grateful that we’ve had the satellite resources in place that have allowed us to track it and document its evolution so closely,” said Shuman. “A-23A faces the same fate as other Antarctic bergs, but its path has been remarkably long and eventful. It’s hard to believe it won’t be with us much longer.”

Even as A-23A fades, other massive bergs are parked or drifting along the Antarctic shoreline. Several, including A-81, B22A, and D15A, are each larger than 1,500 square kilometers and sit waiting for their moment to break free and begin their journey north.

NASA Earth Observatory image by Michala Garrison, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. ISS Astronaut photograph ISS074-E-8943 was acquired on December 27, 2025, with a Nikon Z 9 digital camera using a focal length of 500 millimeters. It is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit at NASA Johnson Space Center. The image was taken by a member of the Expedition 74 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Story by Adam Voiland.