Jan. 21 (Bloomberg) -- A volcano erupted under the Antarctic ice sheet more than 2,000 years ago, a finding that may change predictions of sea-level gains from melting glaciers, scientists reported in the journal Nature.

The Hudson Mountains Subglacial Volcano deposited a layer of ash and rock that now extends across 23,000 square kilometers (8,800 square miles), an area about the size of Massachusetts, the scientists at the British Antarctic Survey found, using radar data gathered from flights above the site. They then used ice core analysis to date the eruption to about the year 325 B.C.

``We believe this was the biggest eruption in Antarctica during the last 10,000 years,'' Hugh Corr, a BAS scientist and lead author of the paper, said in a statement. ``It blew a substantial hole in the ice sheet, and generated a plume of ash and gas that rose around 12 kilometers into air.''

Subglacial volcanoes may be contributing towards the melting of Antarctic ice that is helping speed increases in sea level, the scientists said, adding that the primary cause of melt is probably the warming of the surrounding seas.

The Hudson volcano, which is active, lies close to the southern continent's Pine Island Glacier, whose flow toward the sea has accelerated in recent decades, the scientists said.

``It may be possible that heat from the volcano has caused some of that acceleration,'' David Vaughn, co-author of the paper, said in the statement. ``It cannot explain the more widespread thinning of West Antarctic glaciers that together are contributing nearly 0.2 millimeters per year to sea-level rise. This wider change most probably has its origin in warming ocean waters.''

Increased Snowfall

While scientists in recent years have observed more melting of glaciers in west Antarctica, the continent as a whole may gain mass due to increased snowfall in the east, according to the Nobel Prize-winning United Nations Intergovernmental Panel on Climate Change, which last year produced its most detailed study of global warming in a series of four reports.

The research by Corr and colleagues was published yesterday in Nature Geoscience. The government-funded British Antarctic Survey has an annual budget of 45 million pounds ($88 million), and operates five research stations in and near Antarctica. The group is based in Cambridge, England.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: January 21, 2008 07:25 EST