February 29
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The iceberg named A23a covers an area of about 4,000 square kilometers, and it was originally birthed in 1986 when it calved from the Filchner Ice Shelf. But the hefty berg got stuck soon after when its submerged keel became lodged on the seafloor in the Weddell Sea in West Antarctica, reported Live Science.

A23a has held the title of the world's largest iceberg on multiple occasions as other, more massive ice slabs came and went while it sat in place, Christopher Shuman, a glaciologist at the University of Maryland and NASA's Goddard Space Flight Center, said. 

On November 25, major news outlets reported that A23a had finally started to move. However, the berg's bid for freedom actually began in 2020 when it started to become unstuck from its seafloor tether, the BBC reported. 

Satellite imagery shared on X (formerly known as Twitter) by the British Antarctic Survey shows that A23a finally began moving from its sticking point in January this year. It has since traveled hundreds of miles along Antarctica's coastline. 

A23a became stuck due to the thickness of its ice. Icebergs of this size can be up to 400 meters tall from top to bottom, with around 90% of its mass submerged, Shuman said.   

Being stuck in place for decades is "not uncommon" for icebergs of this size, Shuman said. 

A23a likely became unstuck as ice on its underside melted from below, which reduced its weight and lifted it off the seafloor. This eventually happens to all stranded icebergs and was likely not related to climate change, the BBC reported. 

A23a will be pushed north by ocean currents into the Drake Passage, also known as the iceberg graveyard—a body of water that most other large icebergs born into the Weddell Sea, including A76a and A68a, have passed through on their slow marches to their watery graves. 

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