A detailed geologic map of the volcano will show the distribution of the various volcanic deposits formed by these and other past eruptions, and the work required to generate the map will provide an enhanced account of the volcano's very active eruptive history. A detailed geologic map is a tool for evaluating the volcano's past behavior and determining hazard-mitigation measures. Mount St. Helens is a unique laboratory for studying the processes of explosive volcanoes in the United States and around the world. Because Mount St. Helens is so young and has been so active and so varied in eruptive style, the deposits from its past eruptions are well preserved and yield a rich record of the volcano's history. The answers to that question, in turn, are fundamental for assessing the hazards of active volcanoes throughout the Cascades, Alaska, and the world.
Geologic mapping is a fundamental tool for exploring and documenting a volcano's geologic record.
The geologic map data will provide an unparalleled resource for interpreting the three-dimensional structure of Mount St. Helens. Rapid erosion since 1980 has resulted in new exposures into the flanks of the volcano, and correlation of stratigraphic units from the flanks into the 1980 crater walls is now being undertaken. In combination with geophysical and petrologic data acquired since 1980 on the deep plumbing system of the volcano, we expect to be able to construct unusually accurate cross sections and three-dimensional models of the volcano's internal structure. Our geologic mapping is complemented by stratigraphic analysis of local rock sequences, petrologic studies to evaluate the nature and evolution of the magma that erupted to form the deposits, and radiocarbon and tree-ring dating to establish the chronology of eruptive events. The Mount St. Helens geologic-map project is funded by the U.S. Geological Survey Volcano Hazards and Geothermal Studies Program.