A23a: World's biggest iceberg on the move in the Antarctic Ocean

This satellite imagery, captured by the European Space Agency, shows A23a on the move in Antarctica

The world's biggest iceberg is on the move in the Antarctic Ocean.

Known as A23a, the huge iceberg is around 1,500 sq miles in area - more than twice the size of Greater London.

It split from the Antarctic coastline over 30 years ago, however until recently it had been stuck to the ocean floor.

Scientists say the iceberg has been drifting rapidly for the past year and is about to leave Antarctic waters.

What's happened?

The iceberg had been grounded in Antarctica's Weddell Sea (pictured here)

A23a is not only thought to be the world's biggest iceberg, it's also among the world's oldest.

The huge slab of ice is around 400m thick - that's around the height of 90 double decker buses stacked up on top of each other!

A23a is the largest surviving piece of an iceberg that broke free of the Filchner Ice Shelf in August 1986.

Since then it's largely been stranded after its base became stuck on the floor of the Weddell Sea.

Scientists aren't exactly sure yet why it's finally on the move again after all these years.

British Antarctic Survey glaciologist Oliver Marsh explained: "Over time it's probably just thinned slightly and got that little bit of extra buoyancy that's allowed it to lift off the ocean floor and get pushed by ocean currents."

Marsh also added that experts will be watching its journey closely as it's rare to see an iceberg of this size on the move.

A32a is expected to now move toward the Southern Ocean on a path known as "iceberg alley", where others of its kind can be found bobbing around in dark waters.