Scientists are closely monitoring a series of cracks running through Antarctica’s Brunt Ice Shelf as they prepare for it to release an iceberg roughly 30 times the size of Manhattan.

Satellite images captured at the end of January show a rift that’s steadily been cutting northward is now nearing the edge of the shelf.

Once it reaches this point, an area of ice estimated to be at least 1700 square kilometers (660 square miles) will break free – or, enough to envelope all five boroughs of New York City more than two times over.

Slide the bar to see how the crack has grown from 1986 to 2019

‹ Slide me › Comparisons of images captured by Landsat 8 this year (Jan 23, 2019 pictured right) and Landsat 5 in 1986 (Jan 30, 1896 pictured left) show just how dramatically the situation has changed

WHAT IS A CALVING EVENT? Glacier calving is a natural occurrence caused by the forward motion of a glacier making its end unstable. During a calving event, part of the end of a glacier drops off, often forming an iceberg. Calving of glaciers is often accompanied by a loud cracking or booming sound before blocks of ice up to 60 metres (200 ft) high break loose and crash into the water. The entry of this ice into the water can cause large and hazardous waves. Advertisement

According to NASA, the crack in the Brunt Ice Shelf was stable for nearly 35 years before it recently began accelerating at staggering rates, hitting up to 4 kilometers (2.4 miles) per year.

While it won’t be the largest iceberg to split off from Antarctica by a long shot, it’s the biggest chunk the Brunt Ice Shelf has lost since observations began over 100 years ago in 1915.

And, the ice shelf is the site of year-round research operations at the British Antarctic Survey’s Halley Station, sparking concerns for the humans who work there.

Close-up views of the satellite images show the center rift is stretching across the ice shelf where it will soon meet perpendicularly with two other features: McDonald Ice Rumples and the Halloween Crack.

As of now, the researchers say it’s unclear what exactly will happen.

But, comparisons of images captured by Landsat 8 this year and Landsat 5 in 1986 show just how dramatically the situation has changed.

‘The near-term future of Brunt Ice Shelf likely depends on where the existing rifts merge relative to the McDonald Ice Rumples,’ said Joe MacGregor, a glaciologist at NASA’s Goddard Space Flight Center.

‘If they merge upstream (south) of the McDonald Ice Rumples, then it’s possible that the ice shelf will be destabilized.’

Close-up views of the satellite images show the center rift is stretching across the ice shelf where it will soon meet perpendicularly with two other features: McDonald Ice Rumples and the Halloween Crack

The calving event will affect both the remaining ice shelf and potentially the scientific infrastructure at the remote site.

And, the recent changes in the rift’s activity only add to the questions.

Despite a long period of slow evolution, the past few years have seen significant acceleration.

‘We don’t have a clear picture of what drives the shelf’s periods of advance and retreat through calving,’ said NASA/UMBC glaciologist Chris Shuman.

‘The likely future loss of the ice on the other side of the Halloween Crack suggests that more instability is possible, with associated risk to Halley VIa.’