Antarctic ice shelves at risk of fracturing

The ice shelves ringing Antarctica are vulnerable if rising temperatures drive melt water into the numerous fractures that penetrate their surfaces, according to a new study.

The shelves help slow the slide of glaciers towards the ocean, so if they were to fail sea levels around the world could surge rapidly, the researchers write in the journal Nature.

Most of the shelves are now permanently frozen and stable, but research has shown that even subtle temperature swings could spur widespread melting that would send water surging into the surface fractures.

Such surges would potentially cause hydrofracturing – a process in which water violently forces the fractures to zip open, causing the shelf to rapidly disintegrate

The new study estimates that 50-70% of the areas of the ice shelves buttressing the glaciers are vulnerable to such processes. “It’s not just about melting, but where it’s melting,” says lead author Ching-Yao Lai, from Columbia University, US.

Hydrofracturing has already occurred in a few places, the researchers note. Parts of the Larsen B Ice Shelf, which had been stable for at least 10,000 years, disintegrated within just days in 1995 and 2002, and this was followed by the partial breakup of the Wilkins Ice Shelf in 2008 and 2009.

Working with Google’s Cameron Chen, Lai trained a machine-learning model to identify ice shelf fracture locations across Antarctica, to produce what they say is the first continent-wide map of such features.

Although most fractures contain no liquid water, the researchers considered future cases in which melt water might fully fill them. This allowed them to predict which parts of the shelves would be vulnerable to hydrofracturing, when factoring in the competing forces of compression from the sides and stretching of the ice from back to front.

They calculated that inflow of liquid into the existing fractures could potentially exert enough force to cause widespread hydrofracturing across 50-70% of the ice-shelf areas that provide buttressing.

The main exceptions were smaller, solider areas of ice closest to land, which experience less stress from stretching. The end portions of the shelves, mostly surrounded by open ocean, are also vulnerable, but floating freely as they do, those do not help hold back the glaciers.

The researchers stress that say they cannot predict the ice shelves’ behaviour with any exactitude. It is not clear, they say, how fast melt water would form and fill in the cracks, whether particular locations would undergo hydrofracturing, and whether the process would run away, causing the shelf to undergo explosive Larsen-type disintegration.