Antarctic volcanoes and glacier melting

International Herald Tribune
Antarctic volcanoes identified as a possible culprit in glacier melting
By Kenneth Chang
Sunday, January 20, 2008

Another factor might be contributing to the thinning of some of the Antarctica's glaciers: volcanoes.

In an article published Sunday on the Web site of the journal Nature Geoscience, Hugh Corr and David Vaughan of the British Antarctic Survey report the identification of a layer of volcanic ash and glass shards frozen within an ice sheet in western Antarctica.

"This is the first time we have seen a volcano beneath the ice sheet punch a hole through the ice sheet" in Antarctica, Vaughan said.

Volcanic heat could still be melting ice to water and contributing to thinning and speeding up of the Pine Island glacier, which passes nearby, but Vaughan said he doubted that it could be affecting other glaciers in western Antarctica, which have also thinned in recent years. Most glaciologists, including Vaughan, say that warmer ocean water is the primary cause of thinning.

Volcanically, Antarctica is a fairly quiet place. But sometime around 325 B.C., the researchers said, a hidden and still active volcano erupted, puncturing several hundred yards of ice above it. Ash and shards from the volcano carried through the air and settled onto the surrounding landscape. That layer is now out of sight, hidden beneath the snows that fell during the next 2,300 years.

Still, the layer showed up clearly in airborne radar surveys conducted over the region in 2004 and 2005 by American and British scientists. The reflected radio waves over an elliptical area about 110 miles, or 176 kilometers, wide were so strong that earlier radar surveys had mistakenly identified it as bedrock. Better radar techniques now can detect a second echo from the actual bedrock farther down.

The thickness of ice above the ash layer provided an estimate of the date of the eruption: 207 B.C., give or take 240 years. "It's probably within Alexander the Great's lifetime, but not more precise than that," Vaughan said.