PYROCLASTIC ERUPTIONS OF MOUNT ST. HELENS ON MAY 18, 1980

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The pyroclastic deposits erupted by Mt. St. Helens on May 18, 1980 have been the subject0of intensive study by C. W. Criswell, a PhD student, for the last several years. With the cooperation of the USGS and other academic researchers, he and the PI have mapped a three-dimensional stratigraphic and facies network and correlated it with six eruptive phases, defined by time interval. Chemical and seismic data suggest that two magma types (white and gray) erupted from a zoned magma chamber seven km. deep, and that these changes in the eruptive materials relate to changes in the mechanism of eruption, as well as spatial differences in the magma composition within the chamber prior to eruption." This award will enable Criswell to continue these studies which could have important imlications for predicting future eruptions at Mt. St. Helens and similar volcanoes.