Antarctic A23a iceberg previously 'twice the size of Greater London' may disappear within weeks

A colossal iceberg ranked among the oldest and largest ever recorded is crumbling apart in warm Antarctic waters, and could disappear within weeks.

Earlier this year the "megaberg" named A23a weighed nearly 1 trillion tonnes and was more than twice the size of Greater London, a behemoth unrivalled at the time.

In recent weeks, enormous chunks — some 400 square kilometres in their own right — have broken off.

Smaller chips, many still large enough to threaten ships, have also split, littering the sea around it.

The iceberg is now 1,770 square kilometres, less than half its original size.

"It's basically rotting underneath. The water is way too warm for it to maintain. It's constantly melting," Andrew Meijers, a physical oceanographer from the British Antarctic Survey

said.

"I expect