Countdown to calving at Antarctic ice shelf
Cracks growing across Antarctica’s Brunt Ice Shelf reveal that the shelf is poised to release an iceberg with an area about twice the size of New York City. The crack along the top of the January 23, 2019, image above — the so-called Halloween crack — first appeared in late October 2016 and continues to grow eastward from an area known as the McDonald Ice Rumples (see image below). The more immediate concern is the rift visible in the center of the image. Previously stable for about 35 years, this crack recently started accelerating northward as fast as 2.5 miles (4 km) per year.
It is not yet clear how the remaining ice shelf will respond following the break, posing an uncertain future for scientific infrastructure and a human presence on the shelf that was first established in 1955.
When the fast-growing crack cuts all the way across the ice shelf, the area of ice lost from the shelf will likely be at least 660 square miles (1,700 square km). Although that’s not an enormous iceberg by Antarctic standards, it might be the largest berg to break from the Brunt Ice Shelf since observations began in 1915.
Scientists are watching to see if the loss will trigger the shelf to further change and possibly become unstable or break up. What will happen? Joe MacGregor, a glaciologist at NASA’s Goddard Space Flight Center, said:
The near-term future of Brunt Ice Shelf likely depends on where the existing rifts merge relative to the McDonald Ice Rumples. If they merge upstream (south) of the McDonald Ice Rumples, then it’s possible that the ice shelf will be destabilized.
The growing cracks have prompted safety concerns for people working on the shelf, particularly researchers at the British Antarctic Survey’s Halley Station. This major base for Earth, atmospheric and space science research typically operates year-round, but has been closed down twice in recent years due to unpredictable changes in the ice. The station has also been rebuilt and relocated over the decades.
Calving – the breaking of ice chunks from the edge of a glacier – is a normal part of the life cycle of ice shelves, but the recent changes are unfamiliar in this area. The edge of the Brunt Ice Shelf has evolved slowly since Ernest Shackleton surveyed the Antarctic coast in 1915, but it has been speeding up in the past several years.
Bottom line: Images of growing cracks in the Brunt Ice Shelf in Antarctica, in early 2019, show that the glacier is poised to release a huge iceberg.