World’s Largest, Oldest Iceberg Runs Aground Near Antarctic Island

After a leisurely five-year journey, the ginormous iceberg A23a appears to have run aground near the Southern Ocean’s South Georgia Island, according to the British Antarctic Survey.

A23a weighs nearly a trillion metric tons, making it the world’s largest active iceberg. It calved from Antarctica in 1986, making it the world’s oldest berg. And now, after drifting for half a decade, A23a has grounded itself about 56 miles (90 kilometers) south of South Georgia.

“If the iceberg stays grounded, we don’t expect it to significantly affect the local wildlife of South Georgia,” said Andrew Meijers, an oceanographer at the British Antarctic Survey, in a survey release. “In the last few decades, the many icebergs that end up taking this route through the Southern Ocean soon break up, disperse and melt. Commercial fisheries have been disrupted in the past however, and as the berg breaks into smaller pieces, this might make fishing operations in the area both more difficult and potentially hazardous.”

Graphic showing the iceberg’s path and its position relative to the island. © The Mapping and Geographic Information Centre, British Antarctic Survey

A23a—an iceberg a little larger than the state of Rhode Island—was lodged in the seafloor for decades before it took its wanton journey up to South Georgia. The berg got caught in a water vortex that made its path more predictable, but in 2024 the berg escaped the vortex and it seemed to be on a collision course with South Georgia. Now, the object’s 1,312-foot (400-meter) cliffs are resting south of the island, and may slowly melt and break up on that site.

“From a scientific perspective we are keen to see how the iceberg will affect the local ecosystem,” Meijers added. “Nutrients stirred up by the grounding and from its melt may boost food availability for the whole regional ecosystem, including for charismatic penguins and seals.”

According to a Q&A with Meijers posted on the British Antarctic Survey site, the berg has not yet broken down into smaller chunks, as similar megabergs did in the past.

Because A23a is now grounded, it is more likely to break up. But the berg could yet wriggle free and continue on its northerly tack; Meijers noted that one iceberg came within 620 miles (1000 km) of Perth, Australia, because the warmer waters and air caught up with it and it finally broke up.

For now, A23a is quite easy to track. For one, it’s a gigantic piece of ice, one easily visible to ship operators and even satellites in space. Second, the iceberg is currently stuck in one place. But when A23a begins to break up, the smaller—albeit hazardous—icebergs that splinter off will be much harder to track, which could jeopardize fishing operations.

According to Meijers, Earth’s ice shelves have lost about 6,000 billion metric tons of their mass since 2000. Anthropogenic climate change is expediting the loss of the ice shelves, which has implications for ocean circulation and sea level rise, among other factors.

Scientists are keeping a close eye on the berg—as well as how the local sea creatures react to their newest neighbor.