Researchers have found evidence that a previously undiscovered active volcano, which last erupted about 2300 years ago, could be heating a portion of the West Antarctic Ice Sheet, causing enough melting to nudge the sheet toward the sea. The find is bad news for scientists already worried about the stability of the giant ice sheet as global temperatures climb.
For several decades, researchers have used aerial radar to compile data on the structure and movement of Antarctica's 3-kilometer-thick ice sheets. The ice is extremely clean and therefore transparent to certain types of radio waves, which makes the technique ideal for mapping the ground underneath the sheets. That same technique can also detect wispy deposits of atmospheric contaminants, such as sulfur dioxide, within the ice, revealing, for example, evidence of major volcanic activity on the planet during the past 500,000 years. So far, the radar surveys have covered only a fraction of the continent, however, says glacier geophysicist Hugh Corr of the British Antarctic Survey (BAS) in Cambridge, U.K.
Although several active volcanoes rise above the West Antarctic Ice Sheet, Corr and BAS colleague David Vaughn were still unprepared for what they found: the first evidence of recent volcanic activity under the ice. Analyzing radar data from the West Antarctic Ice Sheet for 2004 and 2005, they found something that had eluded previous researchers: an elliptical zone of dissolved sulfur dioxide about as large as the state of New Jersey. Further analysis, Corr and Vaughn reported online 20 January in Nature Geoscience, revealed that the "dirty" ice was the result of a major volcanic eruption about 325 B.C.E.--probably the biggest volcanic event in Antarctica during the past 10,000 years. The team thinks all the sulfur dioxide came from one eruption because the zone of dirty ice gradually thins out in all directions toward its margins. The evidence leads to a conclusion that there was a single, massive eruption, Corr says.
Furthermore, the volcano's residual heat might still be warming the underside of the ice sheet and speeding up its march toward the ocean, Corr says. And if the volcano does erupt again, much of the sheet could slide into the ocean, adding to already-rising sea levels fueled by global warming. The effect would be even more pronounced if a new eruption occurs, he adds.
The research confirms that there are indeed active volcanoes under the West Antarctic Ice Sheet, says geophysicist Donald Blankenship of the University of Texas, Austin. But what is even more important is how the constant geothermal heating from the volcano is affecting the ice sheet's dynamics. How the meltwater is interacting with the volcanism is "what we need to understand," he says.