Posted by: h4ck@lyst | January 22, 2008

Scientists find active volcano beneath Antarctic ice sheet

Here is another factor that might be contributing to the thinning of some of the Antarctica’s glaciers: volcanoes.
In an article published Sunday on the website of the journal Nature Geoscience, Hugh FJ Corr and David G 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.
For Antarctica, “This is the first time we have seen a volcano beneath the ice sheet punch a hole through the ice sheet,” Dr Vaughan said.
Heat from a volcano could still be melting ice and contributing to the thinning and speeding up of the Pine Island Glacier, which passes nearby, but Dr Vaughan doubted that it could be affecting other glaciers in West Antarctica, which have also thinned in recent years. Most glaciologists, including Vaughan, say that warmer ocean water is the primary cause.

Volcanically, Antarctica is a fairly quiet place. But sometime around 325 BC, 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 over the subsequent 23 centuries.
Although out of sight, the layer showed up clearly in airborne radar surveys conducted over the region in 2004 and 2005 by American and British scientists. The reflected ra
dio waves, over an elliptical area about 110 miles 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 BC, give or take 240 years. For a more pre
cise date, Corr and Vaughan turned to previous observations from ice cores, which contained spikes in the concentration of acids, another byproduct of eruptions. Scientists knew that an eruption occurred around 325 BC, plus or minus a few years, but did not know where the eruption occurred. “We’re fairly confident this is the same eruption,” Vaughan said. NYT NEWS SERVICE

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