Most enduring and biggest iceberg breaks apart, with more splintering to come in its death spiral

An iceberg, known as A23a, top, seen on a NASA satellite, is visible near South Georgia Island, bottom, on Sept. 1, 2025, off the coast of Antarctica. (NASA Worldview via AP)

The world’s largest and most enduring iceberg is splintering into smaller pieces, to the point that it’s no longer the biggest chunk of ice floating in the oceans.

The shrinking megaberg, known as A23A, is unlikely to survive through the end of November and may face a sudden and spectacular collapse like an avalanche of ice at sea, said University of Colorado ice scientist Ted Scambos.

“It’s an interesting thing to watch, certainly not unprecedented,” Scambos said Thursday in an interview with The Associated Press. “But every time these happen, it’s sort of a big spectacular event.”

Because ice shelves already float on water, ice reductions like this won’t raise the sea level. But the reduction in ice shelves will cause melting land glaciers to flow into the oceans, and that causes sea levels to rise a few feet.

A23A first broke away from Antarctica’s Filchner–Ronne Ice Shelf in 1986 along a massive crack that scientist first noticed in the 1950s and called “the Grand Chasm.” It hovered close to the southern continent for about three-and-a-half decades uneventfully until the last couple years, when it drifted north to the place where massive icebergs go to die, around South Georgia Island, Scambos said.

Earlier this year the iceberg was the size of Rhode Island and weighed in at a trillion tons, now it’s down to the size of Houston and shrinking fast. The world’s new biggest iceberg is D15A. It’s nearly twice as big as the shrunken A23A, according to Andrew Meijers of the British Antarctic Survey.

A23A has already spawned smaller chunks named A23D, A23E and A23F. NASA satellite images Thursday show the smaller bergs that weren’t detached on Saturday, just a few days before.

“It’s still quite thick, but it’s a lot thinner than it was when it left the continent,” Scambos said. “And so now it’s being flexed by long period waves, by tides, which sweep across the area. And with that flexing, even though it’s incredibly gentle and subtle. It’s finding weak spots in the iceberg, and those are breaking off.

“I expect its fracturing will accelerate,” Meijers said via email. As the iceberg moves further north and the Antarctic spring begins, Meijers expects by the end of the season, A23A will likely rapidly fall apart into chunks too small to track, he said.

If the iceberg survives the Antarctic spring, the summer looks even more brutal, Scambos said. That’s when it can collapse with warm water even at the top and it will then look “sort of like an avalanche that’s floating” and even fall apart in a single day, he said.

Back in January, Meijers, who visited the iceberg at the end of 2023, painted a different picture of A23A: “The iceberg itself is colossal and it stretches from horizon to horizon ... It’s a huge wall, a Game of Thrones style wall of ice that towers above the ship.”

Megabergs spawning is a natural process that has happened for centuries, Meijers said, and so is their breaking apart around South Georgia Island when the current and warmer waters get hold of them, Scambos said.

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Seth Borenstein, The Associated Press