29-01-2025
- Science
- National Geographic
The world's largest iceberg is on a collision course with vital penguin sanctuary
Seen via satellite on November 28, 2023, A23a was stuck on the seafloor for decades. The massive iceberg ground to a halt in shallow waters.
Photograph By Wanmei Liang, Using MODIS data from NASA
Where did A23a come from?
In 1986, A23a—icebergs are named sequentially based on the Antarctic quadrant in which they were first seen—calved from the Filchner Ice Shelf. Iceberg calving is the natural process of icebergs breaking off from the ice shelf, which happens all the time.
A23a is notable for its size: 'several tens of kilometers in length and a few hundred meters in depth,' says Martin Siegert, a polar scientist at the University of Exeter. 'It's not uncommon, it's not unnatural, but it is unusual because it's just so big; very, very big.'
At just over 1,400 square miles, A23a could currently fill all of New York City, Los Angeles, and Houston combined. Because of its epic proportions, the behemoth 'almost immediately got stuck' on the seabed around the continental shelf, which was too shallow for its keel to pass over, he says.
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'It kept sitting there until about 2020' says Andrew Meijers, science leader of the British Antarctic Survey's polar oceans program. As it lingered, the iceberg gradually melted and was buffeted by winds and ocean currents as chunks of ice tumbled into the water. Eventually, it freed itself into the deep ocean.
