Giant iceberg A23a, once the world’s largest iceberg, finally dies after 40 years at sea, turning into a bright “blue mush”

New satellite images show that once the world’s largest iceberg, A23a, has turned into a beautiful mass of striped “blue mush”, signaling its imminent demise. This moribund ice mass, until recently three times the size of New York City, is one of the oldest ice masses on record and is currently celebrating its 40th anniversary.

A23a is unique among icebergs. Dubbed the “Queen of the Icebergs,” the megaberg broke away from Antarctica’s Filchner-Ronne Ice Sheet in the summer of 1986, but quickly became stuck in place when its submerged bottom caught on the ocean floor. For most of the past 40 years, this ice has remained confined and so close to its parent ice shelf that it has decreased little in size. However, in 2020, A23a finally broke free from its ocean floor restraints and began drifting away from Antarctica.

His journey after that was eventful. First, a huge chunk of ice became trapped again in a huge ocean current, or gyre, and rotated in place for several months. After emerging from the vortex in December 2024, the dizzy burg then headed straight to South Georgia Island, raising concerns among researchers that it could run aground again and pose a potential ecological disaster for the island’s resident penguins. However, this worst-case scenario was averted when A23a began to disintegrate in May 2025, just before reaching the island.

you may like

Since then, the largest remaining chunk of the iceberg has drifted further north into the South Atlantic Ocean, where warm ocean water circulating from South America is taking its toll.

New photos taken by NASA’s Terra satellite on December 26 reveal a completely unrecognizable version of A23a. The iceberg, now about a third of its original size, is shown covered in a blue puddle surrounded by a thick border of white ice called a “castle.” The image also shows a pool of gray sludge, known as ice melange, on the side of A23a, which likely leaked from beneath the iceberg. In addition, it is surrounded by hundreds of small mountains with broken edges.

Image 1/4

A23a was about three times the size of New York City before colliding with South Georgia last year.

A23a (circled) was captured just offshore of the Filchner-Ronne Ice Sheet in Antarctica between 1986 and 2020.

Large chunks have been breaking up over several months as A23a moves into warmer waters.

A23a briefly became stranded off the coast of South Georgia, but soon began to break up and move further north.

Ted Scambos, a climate scientist at the University of Colorado Boulder, said in a NASA statement that the “blue mush” visible on A23a consists of melt ponds that form when surface ice loses its structural integrity. These ponds are streaked, Scambos added, likely caused by “the weight of water trapped in the ice cracks causing the ice to open up.”

Walter Meyer, a senior researcher at the National Snow and Ice Data Center (NSIDC), said in a statement that the cracks likely ran parallel to grooves on the iceberg’s underside, carved into the ice by centuries of movement over the ground while attached to the Filchner-Ronne Ice Sheet. “It’s amazing that these stripes are still there after so many years,” added Chris Schuman, a retired glaciologist at the University of Maryland.

Another photo taken on Dec. 27 by an anonymous astronaut aboard the International Space Station suggests that the bright stripes may already be starting to fade. This subsequent image shows a more uniform pool of blue water on the surface of the iceberg (see below).

It is currently unclear how much A23a remains, or if it has already begun to disappear completely.

A23a has repeatedly held the title of “world’s largest iceberg” throughout its long life due to its persistently huge size.

Most recently, in June 2023, the previous largest iceberg, A-76A, broke apart and regained the title. He then lost the honor again in September 2025, shortly after a matchup against South Georgia State. (Some news outlets incorrectly report that A23a is still the world’s largest iceberg, probably because the Guinness World Records page is outdated.)

According to NSIDC, the world’s largest iceberg is currently D15A, which has a surface area of ​​about 1,200 square miles (3,100 square kilometers), making it several hundred square miles smaller than A23a at its peak.

For more amazing satellite photos and astronaut images, check out Earth from the Space Archives.