Britain has closed down its Halley base in Antarctica as fears grow that an ice shelf the size of Manhattan could break away from the mainland.
Staff have now left the British Antarctic Survey base, departing just days after NASA revealed aerial photos showing an enormous rift in the ice shelf.
The growing chasm is closer to the sea than the Halley base, so it should be largely unaffected.
But scientists can’t be certain and don’t want to leave the base occupied in case staff need evacuating in difficult winter conditions.
“What really matters is what happens upstream of the chasm where Halley is situated,” BAS science director David Vaughan told the BBC.
“We have a network of about 15 GPS stations across the ice shelf surrounding Halley and their data is essentially broadcast to us every day with one day’s lag.
“And although, yes, down by the crack, there are changes – up by Halley, we’ve actually seen very little deformation of the ice.”
BAS has had a permanent research station on the Brunt Ice Shelf since the 1950s.
The structure has been moved around several times since then, as researchers adapt to the changing conditions at the shelf.
But there’s now a major threat to the shelf, as a crack in the ice “accelerates northward as fast as 2.5 miles per year.”
NASA has been tracking the cracks on the shelf using Landsat satellites.
An early image taken in 1986 shows very minimal cracking, but more recent images taken in the last few years show significant breakages in the ice.
The rift along the top of the latest Jan. 23 image is known as the “Halloween crack”, because it first appeared in October 2016.
Since then, it’s continued to grow eastward from an area called the McDonald Ice Rumples, which are crumpled ice that has flown over an underwater formation of bedrock.
But there’s another rift that has NASA even more worried.
The latest image shows a huge crack rising north across the Brunt Ice Shelf.
NASA says this area was stable for about 35 years but is now quickly accelerating by up to 2.5 miles a year.
The rift is now within a couple miles of the McDonald Ice Rumples and the Halloween crack.
And when it finally cuts all the way across, the Brunt Ice Shelf will lose around 1,056 square miles of ice.
This isn’t enormous by Antarctic standards, NASA explains, but it would be the largest berg to break away from the Brunt Ice Shelf since observations began in 1915.
NASA is now watching the shelf closely to see if the loss will trigger a bigger break-up.
“The near-term future of Brunt Ice Shelf likely depends on where the existing rifts merge relative to the McDonald Ice Rumples,” said NASA’s Joe MacGregor.
“If they merge upstream (south) of the McDonald Ice Rumples, then it’s possible that the ice shelf will be destabilized.”
Calving of ice shelves is quite common, but NASA hasn’t seen such significant changes in this area previously.
“We don’t have a clear picture of what drives the shelf’s periods of advance and retreat through calving,” said NASA 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 V1a.”
