The discovery was made by a team led by researchers from Ohio State University who’ve been using GPS to observe vertical motion on the continent since the 1990s. They had previously observed how the lifting of the weight of ice as it melts causes the underlying bedrock to ‘rebound’. But when they looked at the results more closely, they found that the West Antarctic bedrock is being pushed sideways at a rate of up to about 12 millimetres per year.

They weren’t surprised to detect the horizontal motion, but they were surprised by the direction of the movement. ‘From computer models, we knew that the bedrock should rebound as the weight of ice on top of it goes away,’ said Terry Wilson, who leads POLENET, an international collaboration that has placed GPS and seismic sensors across the West Antarctic Ice Sheet. ‘But the rock should spread out from the site where the ice used to be. Instead, we see movement toward places where there was the most ice loss.’

The unusual movement is the result of differences in the mantle regions under East and West Antarctica. By timing the rate at which seismic waves pass under the continent, the researchers found that West Antarctica contains warmer, softer rock, and East Antarctica has colder, harder rock.

This story was published in the February 2014 edition of Geographical Magazine