An ominous-looking fracture has formed in Antarctica’s Brunt Ice Shelf and is edging north towards the McDonald Ice Rumples and Halloween Crack. Glaciologists at NASA’s Goddard Space Flight Center say it threatens to release an iceberg twice the size of New York City.
NASA released an image of the ice shelf from January 23, 2019, revealing two distinct cracks – one inching eastwards and a second heading north. The team compared it to a previous image taken on January 30, 1986, which (noticeably) shows neither of the two cracks.
The crack running horizontally along the top of the ice sheet is called the Halloween Crack because of when it first appeared – the end of October 2016. It extends east from the McDonald Ice Rumples, an unusual formation caused by ice flow over bedrock that touches the underside of the ice shelf. Because the bedrock is so high, it disrupts the flow and results in visible rifts on the ice's surface.
However, it is the second crack, moving south to north at a rate of 4 kilometers (3 miles) a year, that is causing serious concern. It appears to be heading towards the McDonald Ice Rumples.
“The near-term future of Brunt Ice Shelf likely depends on where the existing rifts merge relative to the McDonald Ice Rumples,” Joe MacGregor, a glaciologist at NASA’s Goddard Space Flight Center, said in a statement.
“If they merge upstream (south) of the McDonald Ice Rumples, then it’s possible that the ice shelf will be destabilized.”
NASA explains that calving is a perfectly normal stage in an ice shelf's life cycle, but it is the unfamiliarity of these (relatively) recent changes that are disconcerting. Since Ernest Shackleton surveyed the area in 1915, it has only ever evolved slowly. Now, things are speeding up.
The amount of ice expected to break away from the shelf could be 1,700 square kilometers (660 square miles) or more, NASA says. That is more than twice the size of New York City and roughly one-third of Grand Canyon National Park. A size that is big but not exceptionally big as far as icebergs are concerned. The record (currently) goes to B-15, which spanned almost 11,000 square kilometers (4,250 square miles).
Still, it's concerning, scientists say. It might just be the largest to break away from the Brunt Ice Shelf.
It is also extremely problematic for scientists researching the Brunt Ice Shelf at the British Antarctic Survey’s Halley Station. The base is an important center for Earth, atmospheric, and space science research and is normally up and running all year round. However, in recent years it has had to be temporarily closed twice because of unpredictable changes to the ice. This ice break might force its relocation (again).