Evidence for this comes from a British-American airborne geophysical survey in 2004-5 that used radar to delve deep under the ice sheet to map the terrain beneath.

Vaughan's team spotted anomalous radar reflections over 23,000 square kilometres (8,900 sq. miles), an area bigger than Wales.

They interpret this signal as being a thick layer of ash, rock and glass, formed from fused silica, that the volcano spewed out in its fury.

The amount of material -- 0.31 cubic kilometres (0.07 cubic miles) -- indicates an eruption of between three and four on a yardstick called the Volcanic Explosive Index (VEI).

By comparison, the eruption of Mount St. Helens in 1980, which was greater, rates a VEI of five, and that of Mount Pinatubo in 1991 is a VEI of six.

"We believe this was the biggest eruption in Antarctica during the last 10,000 years," BAS' Hugh Corr says.

"It blew a substantial hole in the icesheet and generated a plume of ash and gas that rose around 12 kms (eight miles

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