[ExI] Massive volcano beneath Antarctic ice

[Damien Broderick]

Massive volcano beneath Antarctic ice

Monday, 21 January 2008
Agençe France-Presse


PARIS: A powerful volcano erupted under the 
icesheet of Antarctica around 2,000 years ago and 
it might still be active today, a finding which 
raises questions about ice loss from the white continent.

The explosive event – rated "severe" to 
"cataclysmic" on an international scale of 
volcanic force – punched a massive breach in the 
icesheet and spat out a plume some 12 kilometres 
into the sky, said British scientists behind the find.

Occasional volcanism

Most of Antarctica is seismically stable. But its 
western part lies on a rift in Earth's crust that 
gives rise to occasional volcanism and geothermal 
heat, occurring on the Antarctic coastal margins.

This is the first evidence for an eruption under 
the ice sheet itself – a slab of frozen water, 
hundreds of metres thick in places, that holds 
most of the world's stock of fresh water.

Reporting in the journal Nature Geoscience this 
week, the investigators from the British 
Antarctic Survey (BAS), In Cambridge, England, 
describe the finding as "unique."

It extends the range of known volcanism in 
Antarctica by some 500 km and raises the question 
whether this or other sub-glacial volcanoes may 
have melted so much ice that global sea levels were affected, they said.

The volcano, located in the Hudson Mountains, 
blew around 207 BC, give or take 240 years, according to their paper.

Anomalous radar readings

Evidence for this comes from a British-American 
airborne geophysical survey completed between 
2004 and 2005. This used radar to delve deep 
under the ice sheet to map the terrain beneath. 
The team spotted anomalous radar reflections over 
23,000 square kilometres - 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 – 
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.

Melting ice

"We believe this was the biggest eruption in 
Antarctica during the last 10,000 years," said 
lead author Hugh Corr. "It blew a substantial 
hole in the icesheet and generated a plume of ash 
and gas that rose around 12 km into the air."

The eruption occurred close to the massive Pine 
Island Glacier, an area where movement of glacial 
ice towards the sea has been accelerating alarmingly in recent decades.

"It may be possible that heat from the volcano 
has caused some of that acceleration," said 
co-author David Vaughan, who stresses though that 
global warming is by far still the most likely culprit.

Volcanic heat "cannot explain the more widespread 
thinning of West Antarctic glaciers that together 
are contributing nearly 0.2mm (0.008 of an inch) 
per year to sea-level rise," he adds. "This wider 
change most probably has its origin in warming ocean waters."