A23A, the onetime king of icebergs, is cracking up — and bowing out

The world’s most famous megaberg is losing its crown. A23A — once the largest and oldest iceberg adrift — is splintering so fast it’s no longer No. 1 and may not survive past November.

“This isn’t unprecedented, but it’s always spectacular,” said University of Colorado ice scientist Ted Scambos, who expects a sudden, avalanche-style collapse at sea if the breakup accelerates.

The British Antarctic Survey’s Andrew Meijers agrees: as A23A drifts farther north and Antarctic spring kicks in, the berg is likely to shatter into pieces too small to track.

A23A has had a wild life. It calved off Antarctica’s Filchner–Ronne Ice Shelf in 1986 along a monster crack known since the 1950s as the “Grand Chasm.” Then it basically parked for three-plus decades, grounded in the Weddell Sea, before finally breaking free and drifting toward the iceberg graveyard near South Georgia Island. Earlier this year it was roughly Rhode Island-sized and weighed about a trillion tons; now it’s closer to the size of Houston and shrinking fast.

The new heavyweight champ is D15A — nearly twice as big as today’s diminished A23A. Meanwhile, the veteran berg is shedding named offspring: A23D, A23E and A23F, with fresh NASA imagery showing more fragments peeling away in recent days.

What’s tearing it apart? Flexing. A23A is still thick, but much thinner than when it left the continent. Long-period ocean swells and tides gently bend the ice, finding every weakness and prying off slabs. If the berg somehow limps through spring, summer’s warmer air and water could finish it in a day, Scambos said — picture an icy skyscraper collapsing into a floating rubble field.

Before this death spiral, A23A was pure spectacle. When Meijers visited late in 2023, he described it as a “Game of Thrones–style wall of ice,” stretching from horizon to horizon. Since then it’s endured an unusually convoluted route: stuck on the seafloor for decades, freed in 2020, spinning in a Taylor-column vortex in 2024, then grounding about 50 miles off South Georgia by March before breaking loose again.

A quick reality check on impacts: because ice shelves already float, A23A’s breakup doesn’t directly raise sea levels. But losing shelves removes the brakes on land-based glaciers behind them, letting more ice flow into the ocean — the stuff that does raise seas over time.

Also important: megabergs calving and dying in warmer waters is a natural, long-running process. Scientists don’t see A23A’s final act as a direct climate-change signal. Still, the data it leaves behind matter. Samples along its path will help researchers understand how these giants alter ocean chemistry, ecosystems and, crucially, the dynamics of the mega-glaciers that control long-term sea-level rise.

For now, the story is simple: after nearly 40 years, the colossus of the Southern Ocean is coming apart — and doing it with a last burst of drama.

With input from the Associated Press, NPR, and USA Today.