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Geologic Publications for Mount Rainier

Three-dimensional geophysical mapping of shallow water saturated altered rocks at Mount Baker, Washington: Implications for slope stability

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Author(s): Carol A. Finn, Maryla Deszcz-Pan, Jessica L. Ball, Benjamin J. Bloss, Burke J. Minsley

Document Type:
Publisher: Journal of Volcanology and Geothermal Research
Published Year: 2018
Volume: 357
Pages: 261 to 275
DOI Identifier: 10.1016/j.jvolgeores.2018.04.013
ISBN Identifier:
Keywords: Electromagnetic Magnetic Volcano hazard Debris flow

Water-saturated hydrothermal alteration reduces the strength of volcanic edifices, increasing the potential for catastrophic sector collapses that can lead to far traveled and destructive debris flows. Intense hydrothermal alteration significantly lowers the resistivity and magnetization of volcanic rock and therefore hydrothermally altered rocks can be identified with helicopter electromagnetic and magnetic measurements. Geophysical models constrained by rock properties and geologic mapping show that intensely altered rock is restricted to two small (500 m diameter), >150 m thick regions around Sherman Crater and Dorr Fumarole Field at Mount Baker, Washington. This distribution of alteration contrasts with much thicker and widespread alteration encompassing the summits of Mounts Adams and Rainier prior to the 5600 year old Osceola collapse, which is most likely due to extreme erosion and the limited duration of summit magmatism at Mount Baker. In addition, the models suggest that the upper ~300 m of rock contains water which could help to lubricate potential debris flows. Slope stability modeling incorporating the geophysically modeled distribution of alteration and water indicates that the most likely and largest (~0.1 km3) collapses are from the east side of Sherman Crater. Alteration at Dorr Fumarole Field raises the collapse hazard there, but not significantly because of its lower slope angles. Geochemistry and analogs from other volcanoes suggest a model for the edifice hydrothermal system.

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Suggested Citations:
In Text Citation:
Finn and others (2018) or (Finn et al., 2018)

References Citation:
Finn, C.A., M. Deszcz-Pan, J.L. Ball, B.J. Bloss, and B.J. Minsley, 2018, Three-dimensional geophysical mapping of shallow water saturated altered rocks at Mount Baker, Washington: Implications for slope stability: Journal of Volcanology and Geothermal Research, Vol. 357, pp. 261-275, doi: 10.1016/j.jvolgeores.2018.04.013.