Mega-iceberg A23a, formerly the world’s largest, turns into bright ‘blue mush’ as it finally dies after 40 years at sea
The world’s former largest iceberg, A23a, has been transformed into a beautiful patch of striped “blue mush”, signaling its impending demise, new satellite photos reveal. The disappearing ice mass, which until recently was three times the size of New York City, is one of the oldest icebergs on record, and is now approaching its 40th anniversary.
A23a is an oddity among icebergs. The megaberg, nicknamed the “queen of icebergs,” broke away from Antarctica’s Filchner-Ronne ice sheet in the summer of 1986, but quickly became stuck when its submerged bottom clung to the seafloor. It has remained trapped for most of the past four decades, barely decreasing in size due to its proximity to its original ice shelf. However, A23a ultimately freed itself from its attachment to the seabed in 2020 and began moving away from Antarctica.
Since then, the largest remaining part of the iceberg has drifted further north into the South Atlantic Ocean, where warmer waters circulating from South America are wreaking havoc.
New photos, taken on December 26 by NASA’s Terra satellite, reveal a completely unrecognizable version of the A23a. The iceberg, which is now about a third of its original size, is shown covered in pools of blue water surrounded by thick rims of white ice, nicknamed “ramparts.” In the image, A23a is also flanked by a pool of gray mud, known as ice melange, which likely escaped from beneath the iceberg. It is also surrounded by hundreds of small icebergs that have broken off its edges.
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The “blue slush” visible on A23a consists of melt pools, which form when surface ice loses its structural integrity, Ted Scambosa climatologist from the University of Colorado at Boulder, said in a NASA statement. These ponds line up in streaks, likely caused by “the weight of water sitting inside the cracks in the ice and forcing them open,” Scambos added.
The cracks likely parallel grooves beneath the iceberg, which were carved into the ice by centuries of movement on the ground while still attached to the Filchner-Ronne ice sheet, Walter Meiersaid a senior research scientist at the National Snow & Ice Data Center (NSIDC), in the release. “It’s impressive that these streaks still appear after so long,” added Chris Shumanretired glaciologist, formerly of the University of Maryland.
The vibrant streaks may have already started to disappear, according to another photo taken Dec. 27 by an anonymous astronaut aboard the International Space Station. This next 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 whether it has already started to disappear completely.
Due to its massive and persistent size, A23a has repeatedly held the title of “world’s largest iceberg” throughout its long lifespan.
He recently regained the title in June 2023, when the The former largest iceberg, the A-76A, broke apart; so, that I lost the distinction again in September 2025, shortly after its meeting with South Georgia. (Some points of sale having made false statements that A23a remains the largest iceberg in the world, probably due to an outdated page of Guinness World Records.)
The world’s current largest iceberg is now D15A, which has an area of about 1,200 square miles (3,100 square kilometers), according to NSIDCmaking it a few hundred square kilometers smaller than the A23a at its peak.
For more incredible satellite photos and astronaut images, check out our Earth seen from space archives.
