Explosive volcano highlights eruption risk
The violent eruption of a Patagonian volcano last year has shown the high speed with which magma can burst through the earth's crust, according to a European study.
The finding has prompted warnings for closer monitoring of potentially active volcanoes around the world.
The unexpected explosive eruption of the Chaitežn volcano in Chile on 1 May 2008, occurred less than 24 hours after residents in the nearby town of Chaitežn first began feeling earth tremors. The force of the eruption resulted in ash being deposited across Chile and large parts of southern Argentine.
An examination of the forces behind the eruption published in the journal Nature, shows that the magma travelled at up to 1 metre per second.
It shot from a depth of more than five kilometres to the surface in about four hours. This compares with the months to years of seismic unrest that precedes most eruptions.
The Chaitežn eruption is of particular interest because it was a rhyolitic explosive eruption - a rare volcanic event. Rhyolite is a volcanic material high in silica, which tends to make it very viscous or sticky and prone to explosive eruptions caused by trapped gasses.
Depending on the nature of the eruption it can form pumice or obsidian on the surface.
The violent and unexpected nature of the blasts, together with their rarity, means the Chaitežn eruption is the first rhyolite event to have been scientifically assessed in this way.
Australian geologist, Dr Wally Johnson of the Australian National University in Canberra is currently studying a rhyolitic eruption that occurred thousands of years ago at the Rabaul volcano in Papua New Guinea. He says the analysis of the Chaitežn eruption is strong.
Johnson says the last explosive rhyolitic eruption occurred in 1912 when the Novarupta volcano spewed 30 cubic kilometres of magma in 60 hours.
"But when they do take place, they're highly explosive and for anyone living nearby they're certainly dangerous."
Professor Donald Dingwell of the Ludwig-Maximilians Universitaet in Germany and Jonathan Castro of the French Centre National de la Recherche Scientifique (CNRS), analysed the crystal content of the extensive ash deposits around the Chaitežn Volcano to determine the pressure, temperature and water content of the magma as it rose to the surface.
By documenting the speed with which the magma reached the surface, the researchers have now provided a measure for comparing the activity of other rhyolite volcanoes.
"They put up a very, very good case for rhyolitic magma ascending very quickly through the crust," says Johnson. "Basically once it starts, it's on its way and there's not much chance of getting a reasonably early warning."
Johnson says that while rhyolite volcanoes are rare, there should be increased monitoring of potentially active volcanoes, in particular in developing countries, regardless of the magma involved.