Earthquakes often precede explosive volcanic eruptions such as the devastating outburst from Mount St. Helens in 1980. But attempts to use tremors to predict the timing and force of such explosions have proved unsuccessful for decades. Now multidisciplinary teams of researchers have developed models that could help warn of disastrous eruptions hours to days before they happen.
A group of scientists at the University of Leeds in England investigated the mystery of why volcanic tremors come in clusters and why they can occur at multiple depths within volcanoes. The answer may lie in how magma behaves: much like Silly Putty, it shatters if pulled apart quickly. When magma rising within a volcano’s main conduit ruptures, the magma develops deep cracks. These cracks weaken the magma, helping it rupture at other points and flow more quickly, which causes still more shattering to occur.
Such a series of ruptures may explain the swarms of low-frequency earthquakes that past research has detected from volcanoes. Analysis of such tremors could determine how fast magma is ascending “and thus can be used to forecast explosions,” says geophysicist Jürgen Neuberg of Leeds. Neuberg and his Leeds colleague Mark Thomas detailed their findings online March 2 in Geology.
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A model developed by another team considers tremors created by columns of magma within a volcano that wag back and forth within its main conduit like a metronome rod. The rate at which the magma wagging occurs matches the dominant frequency of most volcanic tremors, reports volcanologist and geophysicist Mark Jellinek of the University of British Columbia, who described his team’s work in the February 24, 2011, issue of Nature. (Scientific American is part of Nature Publishing Group.)
As explosive eruptions near, this model indicates the volcanic tremor frequency would rise in a predictable manner: explosive eruptions would generate gas that would constrict the magma column into a stiffer, thinner shape that would wobble faster. Both research teams say they need to further refine their models with additional data from volcanoes. Any future attempts to predict explosive eruptions will also need to look at changes in gas emissions and how volcanoes physically deform before explosions. “If we take all these data together, we might be able to prevent tragedies,” Neuberg says.
This article was published in print as "Thar She Blows!"