On February 20, 2019, NASA Earth Observatory shared images of the ice shelf, comparing a satellite view from Jan. 23 this year to another image taken on Jan. 30, 1986.
According to the NASA report, the crack along the top of the January 23 image—the so-called Halloween crack—first appeared in late October 2016 and continues to grow eastward. The immediate concern right now is the rift visible in the center of the image.
Previously stable for about 35 years, this crack has started spreading northward at an accelerated rate of about 4 kilometers (2.5 miles) a year. The Halloween crack is also lengthening by nearly 4 kilometers a year. The fracture moving in a northward direction has only about 3 miles to go before reaching the Halloween crack.
It is easy to see the long fracture in the ice in the 2019 image as it snakes from south to north, covering almost the length of the ice shelf. If you look closely, you can also see the Halloween crack extending from west to east up near the McDonald Ice Rumples.
NASA says 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.” The British Antarctic Survey has had a presence on the ice shelf since 1956 when they set up the Halley Research Station.
Over the years since it was established, the research station has been moved several times due to the threat posed by chasms and cracks in the ice. The Halley Research Station was last moved in 2017 due to the growth of two chasms in the ice shelf.
The McDonald Ice Rumples
The McDonald Ice Rumples is also playing a part in the drama unfolding on the Brunt Ice Shelf. Rumples are formed when ice flows over a rocky formation where the bedrock rises high enough to contact the underside of the ice shelf. This rocky formation impedes the flow of ice and causes pressure waves, crevasses, and rifts to form at the surface. None of those are good for stability.
“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.”
Calving is a normal part of the life cycle of ice shelves, but the recent changes are unfamiliar in this area. Actually, the edge of the Brunt Ice Shelf has experienced very little change since it was surveyed by Ernest Shackleton in 1915, but it has been speeding up in the past several years.
The uncertainty over what will happen in the future leaves researchers at the British Antarctic Survey’s Halley Station very concerned, especially after it has been closed down twice in recent years due to unpredictable changes in the ice. NASA/UMBC glaciologist Chris Shuman says, “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.”
