What We Know About The World's Biggest Iceberg

Icebergs can get really, really big. In 2019, an iceberg twice the size of New York City started to break free from Antarctica, but shockingly, this wasn't even close to the largest iceberg in the world. There's an iceberg that's not just bigger than the city; it's a little bigger than all of Long Island. The whopping 1,418 square mile mass of ice known to scientists as A23a has held the record of world's biggest iceberg for more than three decades, but now its time at the top is ending.

A23a began its journey as a part of the Filchner-Ronne ice shelf on the Atlantic coast of Antarctica. In 1986, it broke away from the continent, tumbling into the waters below. Its incredible surface area was stunning, but as they say, that was only the tip of the iceberg. Accounting for the full mass, researchers estimated A23a's weight at more than one trillion tons.

After A23a broke away from the Antarctic landmass, it began to float north, but it didn't get far. It turns out the iceberg was so large that its bottom scraped against the sea floor. This caused A23a to get stuck in the Weddell Sea, an inlet adjacent to the Antarctic Peninsula, not far from where the Atlantic and Pacific Oceans meet. It stayed there for nearly 40 years, becoming not only the largest, but also the oldest iceberg in the world. However, it appears that A23a's remarkably long life is now coming to a close.

Nothing lasts forever, even inanimate objects. As A23a sat grounded in the Weddell Sea, the waters swirling around it caused the ice to gradually disintegrate. In 2020, it lost its hold on the seafloor and began to float away. Over the next five years, it was halted twice more, once in a vortex of ocean currents known as a Taylor column, which caused A23a to spin in place for months before breaking loose again. This was followed by another grounding on the continental shelf, but this halt would only last two months, and in May of 2025, A23a began to drift further and further away.

As A23a moved northward, the waters around it became warmer, rising above the freezing levels that kept the iceberg alive for so long. As the temperature climbed, A23a began to disintegrate at a rapid pace, and by the end of the summer, it had lost more than half of its original mass. In doing so, A23a lost the title of the world's largest iceberg, and while it still remains the oldest, it is shrinking at an ever faster rate, and it won't survive much longer.

This turn of events means that a new iceberg has claimed the record for size. It's called D15a, and at 1,158 square miles, it comes short of A23a, but still, that's nearly twice the size of Greater London. And size isn't the only thing that can make an iceberg remarkable. A strangely-shaped iceberg offers just as much to learn from.