Giant Antarctic iceberg breaks into the sea after forming ominous crack

Crack.

Antarctica's retreating Pine Island glacier in late September, about 115 square miles of ice – an area more

The single largest chunk of ice is four times the size of Manhattan.

This iceberg calving event reinforces a continuing story of the melting and retreating of Antarctic glaciers, particularly due to relatively warm oceans eating away at the ice from below.

Stef Lhermitte, a geoscientist specializing in remote sensing at the Netherlands, said: "This retreat and weakening is almost entirely driven by a thinning driven by ocean melting at the bottom.

This latest calving – while significant – was the sixth-largest event of its kind in the Pine Island Glacier since 2001.

Ice shelves – which are the end of massive Antarctic glaciers that float over the ocean – regularly break into the sea.

But today, with ice thinning from below, the ice is breaking into the sea than can be naturally replenished.

"At the beginning of the 2000's it was about every 6 years, but the frequency of calving has increased since 2013," said Lhermitte.

"The resulting icebergs also disintegrate more rapidly as we arrived with yesterday's iceberg."

These ice shelves matter, a lot.

Specifically, they act as plugs, often pinning to the seafloor and holding back Antarctica's formidable ice sheets from flowing unimpeded into the ocean.

With more ice retreat, like this latest instance, the ice shelf is more vulnerable to collapse.

In short, the plug may disintegrate in the ocean which could eventually be unleash yards – not feet – of sea level rise.

Such major collapses are relatively new and largely unprecedented in human history, so it's unknown how quickly this might happen – perhaps this century, or soon after.

NASA oceanographer Josh Willis said in September, "We really do not know for sure how fast they are going to collapse.