NASA’s high-flying observational instruments are great at peering deep into space, but the agency also spends plenty of time staring down at our own planet, too. NASA has been hard at work in recent decades developing models and recording observations that show what’s happening to Earth, and now scientists are warning that a huge ice chunk is about to free itself from Antarctica.

A colossal crack forming on the Brunt Ice Shelf in Antarctica will soon cleave a chunk of ice twice the size of New York City, NASA says, and the increasingly unpredictable nature of the ice in the area could threaten research stations that have operated in the this part of Antarctica for decades.

In images captured by NASA’s Landsat satellites we can see cracks stretching for huge distances on the shelf. The large “Halloween crack,” as it is called, has been growing since 2016, while a separate crevice is currently stretching up to meet it. Once the cracks merge the huge iceberg will be released into the ocean.

A research settlement operated by the British Antarctic Survey is of immediate concern during this dramatic event. It’s located not far from the two growing cracks, and when the ice breaks free nobody knows how it will affect the stability of the ice leading up to the settlement itself. NASA notes that the station has had to be occasionally abandoned in recent years due to the threat of unstable ice.

The chunk that is about to be set free spans some 660 square miles. That’s big by anyone’s standards, and it’ll be the largest piece of ice to break free from the Brunt  Ice Shelf since scientists began keeping track of such things. It may not hold a candle to much larger icebergs that have broken loose in other areas of Antarctica, but it’s yet another reminder that we’re losing this ice at a faster rate than it can regenerate.