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Friday, December 12, 2008

Champagne effect could help to predict volcanoes, says University of Oxford

The Anak Krakatau volcano

Earthquakes can set off volcanoes by shaking up molten rock like champagne in a bottle until they explode, a study suggests. The research shows that volcanoes erupt up to four times more often after a large earthquake than they would without the seismic agitation.

The effects of an earthquake can be felt hundreds of miles from the epicentre and are powerful enough to wake dormant volcanoes. However, it can take so long for a surge of molten rock to build up enough pressure to cause an eruption that several months can elapse between the trigger and the volcanic explosion.

The link between volcanoes and earthquakes has long been suspected but the new research has provided the first statistical evidence. Researchers at the University of Oxford identified the champagne effect after analysing records of volcanoes and earthquakes in southern Chile, the region where Charles Darwin first speculated on the likely link in 1835.

The research team found that the pattern of eruptions over the past 150 years showed a noticeable increase for a year after large earthquakes.

The volcano Tupungatito erupted within a year of both the 1906 and 1960 earthquakes, as did Calbuco and Villarrica. Osorno and Puntiagudo both erupted soon after Chile’s 1837 earthquake.

“The most unexpected part of this discovery was the considerable distance from the earthquake rupture where these eruptions took place, and the length of time for which we saw increased volcanic activity,” said Sebastian Watt, one of the researchers.

This suggests that seismic waves, radiating from the earthquake rupture, may trigger an eruption by stirring or shaking the molten rock beneath volcanoes.

“The disturbances that result from this lead to eruption but, because of the time it takes for pressure to build up inside a volcano and for magma to move towards the surface, an eruption may not occur until some months after the earthquake.”

There was a particularly strong effect in the wake of the great Chilean earthquake of 1960, the largest ever recorded with a magnitude of 9.5 on the Richter scale. The estimated death toll varies from 1,655 to 5,700, many of whom died because the quake prompted tsunamis in several countries.

Another of the earthquakes shown to have been followed by a succession of at least six volcanoes was that of 1906. In an average year just one volcano would have been expected.

"This work is important because it shows that the risk of volcanic eruption increases dramatically following large earthquakes in parts of the world, such as Chile, affected by these phenomena.

“Hopefully, our findings could help governments and aid agencies to manage volcanic hazards by showing the need for increased awareness of volcanic activity after large earthquakes.”

A report of the findings is to be published in the journal Earth and Planetary Science Letters.

Original here

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