Study provides fresh insight on volcanic eruptions

Chemical signatures provide picture of internal changes leading to the 1980 eruption of Mount St. Helens

New tools for monitoring volcanoes may be developed with help from a study on Mount St. Helens published this week (Oct. 14) in Science Express by an international team of geoscientists, including University of Oregon volcanologist Katharine Cashman.
The study on geochemical precursors to volcanic activity leading to the cataclysmic eruption of the southwestern Washington mountain in 1980 yields new insight about volcano behavior. “We’re looking at chemical signatures–chemistry that’s related to volatile, or gas, phases in the eruptive cycle,” says Cashman, a professor of geological sciences. “We’ve learned that the magma that erupted on May 18, 1980, had probably begun degassing for a minimum of five years before the eruption,” she explains. “Then, throughout the summer of 1980, what we see is evidence that gas from the deeper magma storage system had been interacting with the magma at a shallower level.”

The study provides a detailed picture of magma and gas movement during 1980. The data shows that ascending magma stalled and was stored at a depth of three to four kilometers beneath the surface.

Cashman’s in-depth knowledge of Mount St. Helens began when she served as the U.S. Geological Survey spokesperson before, during and after the 1980 eruption. Since then, she’s become an authority on volcanoes from Hawaii to Italy, where she had intended to spend the current academic year working with Italian volcanologists to compare eruptive styles at Etna, Stromboli and Vesuvius with those of the Cascades. She flew back from Italy last weekend to rejoin colleagues at Mount St. Helens where her role is to “be eyes and corporate memory from the ’80s so we can make comparisons between then and now.”

This week’s ScienceExpress publication follows on the heels of a Geology magazine article (February 2004) by Cashman and Richard Hoblitt of the Hawaiian Volcano Observatory which reported that the ash Mount St. Helens spewed during the months before its huge 1980 eruption contains tiny crystals that show an explosive eruption was likely.

Cashman, whose research interests include volcanology, igneous petrology and crystallization kinetics, joined the UO faculty in 1991. Her work is funded by the National Science Foundation.