The layer is buried in the middle of the ice sheet that covers the volcano, roughly 1,000 feet (300 meters) deep under the ice's surface.
This depth, along with thin acid layers that showed up in ice cores from distant parts of western Antarctica, suggest that the volcano erupted around 300 B.C.
(Watch a video of an erupting volcano.)
Heat from the volcano likely melted a large amount of ice around it, and this meltwater probably ran under the base of the ice sheet and out to sea, the researchers say.
The volcano could continue to melt ice around it, and the meltwater could lubricate the base of the ice sheet, speeding up the movement of the nearby Pine Island Glacier, helping make it today one of Antarctica's fastest-flowing glaciers.
(Related: "Buried Lakes Send Antarctica's Ice Slipping Faster Into the Sea, Study Shows" [February 21, 2007].)
"The presence of the volcano adds [to] the complexity of an issue that I thought we were getting on top of," Vaughan said.
Western Antarctica "is losing ice to the oceans, and the volcano could be contributing to that effect."
But it can only be responsible for a fraction of that change, he added, since the volcano only affects the nearby Pine Island Glacier.
Global warming is still the main culprit behind the overall loss of ice from western Antarctica, researchers say.
Subglacial Hot Plate
Magnús Guðmundsson, of the University of Iceland in Reykjavik, says the new study is "quite convincing."
In Iceland frequent volcanoes under glaciers haven't disrupted the ice too much. But it may be different for large ice sheets such as those in Antarctica, said Guðmundsson, who was not involved in the study.
"By finding the site of a recent Antarctic eruption, it may be possible to study if and how this eruption affected the ice flow," he added.
Robin Bell, of the Lamont-Doherty Earth Observatory in Palisades, New York, was also not involved in the new research.
"We have not really thought through the implication of a hot plate that turns off and on beneath the ice sheet," Bell said.
But she believes it could have effects on the ice sheet that researchers need to take into account."What is remarkable now," Bell added, "is that it is becoming more broadly accepted that what is under the ice sheet does matter."
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