Triggering Of Volcanic Eruptions

In a paper published last week in the journal Nature, Alan T. Linde and I. Selwyn Sacks, scientists at the Carnegie Institution's Department of Terrestrial Magnetism in Washington, D.C., assert that there is a pressing need to continuously monitor, using high-sensitivity methods, the deformation of active volcanoes. These small deformations, caused by seismic wave disturbances of the subterranean magma chambers, may point to a volcano's imminent eruption.

While earthquakes and volcanoes result from the large-scale effects of plate tectonics, it has generally been thought that particular instances of earthquakes and eruptions are not directly related. But, upon noting the relationship between the 1992 Landers (southern California) earthquake and the ensuing seismicity and deformations at eastern California's Long Valley Caldera, Linde and Sacks undertook a study to investigate a possible link between earthquakes, small deformations, and potential volcanic eruptions. By examining the historical record of volcanic eruptions and earthquakes (using catalogs of the Smithsonian Institution's Global Volcanism Network and the U. S. Geological Survey's National Earthquake Information Center), the authors show a statistically significant correlation between large magnitude (greater than or equal to 7.0 on the Richter scale) earthquakes and volcanic eruptions separated by a distance up to 750 km. They exclude the phenomenon of volcanic earthquakes (small-magnitude seismicity or earthquakes accompanying eruptions) by considering only large-magnitude earthquakes, and use only explosive-type (as opposed to eruptions with a very fluid lava) eruptions in the data sets. The time frame between earthquakes and eruptions must be within a few days. Volcanic earthquakes are excluded because they are not the cause of eruptions, merely a symptom of an eruption. The authors display their results graphically, and use a variation of bootstrap analysis to show that the effect is not simply due to chance.

Linde and Sacks also point out that within two days following an initial volcanic eruption, a subsequent eruption at a second volcano (up to 200 km distant) occurs much more frequently than would be randomly expected. This second, or paired eruption, may be caused by the passage of seismic waves from earthquakes associated with the primary eruption. These seismic waves may cause a pressure increase in the magma chambers, and if the pressure is already at a critical stage, an eruption may follow.

The authors feel it is important to increase geophysical monitoring at active volcanoes, using high-resolution strainmeters and tiltmeters installed in boreholes deep within the volcano. By watching even the smallest deformations of volcanoes, scientists may be able to predict volcanic activity more accurately and warn populations of impending eruptions. "This is a huge area where a lot of work is needed. Volcanoes give signs about when they are going to go off," says lead author Alan Linde. Their paper shows that a correlation does exist between strong earthquakes, the triggered deformation of volcanoes, and eruptions. By adding high-sensitivity data from monitoring instruments, scientists, in the future, will have new insights into the volcanic eruption process.

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The Department of Terrestrial Magnetism (DTM), led by Sean S. Solomon, is one of five research arms of the Carnegie Institution of Washington, a nonprofit organization devoted to basic research and education in the physical and biological sciences. Scientists at DTM are engaged in studies in seismology, geochemistry, and the astronomical and planetary sciences. Other Carnegie departments are the Geophysical Laboratory, co-located with DTM in northwest Washington, D.C.; the Department of Plant Biology, in Stanford, CA; the Department of Embryology, in Baltimore, MD; and the Carnegie Observatories, in Pasadena, CA, and Las Campanas, Chile. The institution's president is Maxine F. Singer.