First Subglacial Eruption Found in Antarctica

Jan. 21, 2008 — -- The first evidence of a volcanic eruption beneath Antarctica's ice has been discovered by scientists.

Some 2,000 years ago, a volcanic eruption blew a large hole through hundreds of kilometers of the West Antarctic ice sheet, spewing debris into the atmosphere, say the researchers. And the evidence of the explosion they uncovered suggests this was the biggest eruption Antarctica has seen in the last 10,000 years.

The discovery could also explain why a fast-moving nearby glacier has experienced sudden jolts in its journey towards the sea.

West Antarctica rests on a tectonic rift. Several volcanoes protrude through the ice, including the world's southernmost active volcano, Mount Erebus.

But a subglacial volcano -- one that is locked beneath several hundred metres of ice -- is much harder to detect because the ice conceals the volcanic cone.

Hugh Corr and David Vaughan of the British Antarctic Survey made their discovery using a powerful radar system.

Flying over the Hudson Mountains, which separate the East and West Antarctic ice sheets, they detected a layer of debris the size of New Hampshire in the US (23,000 square kilometres), between 100 and 700 meters beneath the surface of the ice.

The radar signal had been noticed before. But it is so strong that previous researchers had thought that it must be bedrock and mapped it as the bottom of the ice sheet on that assumption.

Corr and Vaughan's radar allowed them to see through the signal to the real bedrock beneath. They deduced that instead of marking the bottom of the ice sheet, the signal comes from a layer of debris, 0.3 millimetres at its thinnest, suspended in the ice.

The elliptical shape of the layer, the fact that it thins towards the edges, and the fact that all of the debris was deposited at the same time led the researchers to conclude that this must be a fine sheet of volcanic debris that was propelled into the air by an eruption and settled back down on the ice around the volcano.