December 9, 2008

Earthquakes Could Trigger Volcanic Eruptions

A controversial new study based on findings from an analysis of records in southern Chile suggests that very large earthquakes can trigger an increase in activity in nearby volcanoes.

The researchers noticed that up to four times as many volcanic eruptions occurred during the year following very large earthquakes than did so in other years. They say volcanoes around 300 miles away from an earthquake's epicenter were affected.

In the past, scientists had identified only a few cases where volcanic eruptions followed very large earthquakes.

However, it's hard to show statistically that these earthquakes were the cause of an increase in eruptions, rather than coincidences. So far, the idea is not widely accepted among scientists.

The research team studied the volcanic eruption and earthquake records of southern Chile where, in 1835, Charles Darwin first speculated on the link between earthquakes and eruptions.

Sebastian Watt and Oxford colleagues David Pyle and Tamsin Mather analyzed historical records and discovered that volcanic activity increased for about a year after each of the largest earthquakes in southern Chile - those greater than 8.0 magnitude - over the past 150 years.

It was unexpected to find eruptions occurring so far from the earthquake rupture zone and also the length of time over which increased volcanic activity was seen, Watts said.

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

"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 the magma to move towards the surface, an eruption may not occur until some months after the earthquake."

The volcanoes most likely to be affected lay within 300 miles of the earthquake epicenter, and included both dormant and active volcanoes.

The Chilean earthquakes in 1906 and 1960 - the latter, a 9.5 magnitude event, was the largest earthquake ever recorded - were each followed by activity at six or seven volcanoes. The researchers say this represents a significant increase on the average eruption rate of about one per year.

"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," said Watts.

Studies in the past concluded that wherever a volcano is primed, the specific timing of an eruption could be triggered by seismic activity. But other experts say the idea is not "widely held" among the volcanology community.


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