Post by Urban Warrior on Jan 23, 2008 6:39:19 GMT
Huge volcano erupted under the Antarctic ice
Submitted by Da Verminator:
A powerful volcano erupted under the icesheet of West Antarctica around 2 000 years ago and it might still be active today - a finding that prompts questions about ice loss from the white continent, British scientists report on Sunday. 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 12 000m into the sky, they calculate. 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 - the 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, the investigators from the British Antarctic Survey (BAS) describe the finding as "unique." It extends the range of known volcanism in Antarctica by 500km and raises the question whether this or other sub-glacial volcanoes may have melted so much ice that global sea levels were affected, they say. The volcano, located in the Hudson Mountains, blew around 207 BC, plus or minus 240 years, according to their paper. 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, 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 - indicated 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.
Submitted by Da Verminator:
A powerful volcano erupted under the icesheet of West Antarctica around 2 000 years ago and it might still be active today - a finding that prompts questions about ice loss from the white continent, British scientists report on Sunday. 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 12 000m into the sky, they calculate. 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 - the 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, the investigators from the British Antarctic Survey (BAS) describe the finding as "unique." It extends the range of known volcanism in Antarctica by 500km and raises the question whether this or other sub-glacial volcanoes may have melted so much ice that global sea levels were affected, they say. The volcano, located in the Hudson Mountains, blew around 207 BC, plus or minus 240 years, according to their paper. 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, 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 - indicated 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.