In 1986, a massive iceberg, more than three times larger than New York City, calved off West Antarctica’s Filchner-Ronne Ice Shelf and immediately grounded on the floor of the Weddell Sea, where it remained stuck for almost four decades.

In November, the iceberg, designated A23a, broke free from the sea bottom and began drifting on the Antarctic Circumpolar Current into “iceberg alley”. Satellite images showed the berg, weighing nearly a trillion metric tonnes, drifting quickly past the northern tip of the Antarctic Peninsula, aided by strong winds and currents.

The iceberg, which some scientists are referring to as a “megaberg,” is currently the world’s largest and among the world’s oldest icebergs. As it drifts, it is being eroded by waves and is melting in the relatively warmer waters of the Southern Ocean. The impact of the waves has carved huge arches and caves in the 400-meter-high walls of the iceberg.

Experts are watching to see how close A23a gets to the British Overseas Territory of South Georgia. If it drifts into the island it could do considerable damage to the ecosystem. 

In 2020, an iceberg A68a, comparably sized to A23a, was drifting on a collision course with South Georgia Island. If the berg ran aground offshore of the island, it would pose a grave threat to local penguins and seals on the island as well as to creatures living on the seafloor. Fortunately, A68a broke up in the slightly warmer waters of the Southern Ocean before it could drift into the island.

Only time will tell if the massive A23a melts and breaks up before threatening the island.

Thanks to David Rye for contributing to this post.