HR: 0830h
AN: V51F-0337    [PDF]
TI: Influence of the Geotechnical Properties of Dacite Domes on the 1980 Failure of Mt. St. Helens
AU: * Katzenstein, K W
EM: kurt@intercomm.com
AF: University of Nevada Reno, Department of Geological Scinces, Mail Stop 172, Reno, NV 89557 United States
AU: Watters, R J
EM: watters@mines.unr.edu
AF: University of Nevada Reno, Department of Geological Scinces, Mail Stop 172, Reno, NV 89557 United States
AB: The largest historical rockslide-avalanche occurred on May 18th, 1980 as part of the eruption of Mt. St. Helens. The slide had a volume of approximately 2.8 km$^{3}$, and decreased the elevation of the volcano by about 400 m. The flank collapse prompted a reappraisal of theories regarding volcano morphology, construction, and hazard assessment. Previous stability assessments of the volcano used small-scale (36 cm$^{2}$) shear tests on the reworked avalanche deposits to obtain strength data. Our approach utilized strength data from 1) large (0.15 m$^{2}$) and small-scale shear testing on reworked avalanche deposits, 2) uniaxial, triaxial and joint shear strength of collected in-situ samples of fractured domes and associated dykes, and 3) calculated or back - analyzed strength values of the 1980 cryptodome. Field investigations included collection of data from safe, accessible areas within the crater, breach and summit rim. Field mapping, photogrammetry, spatial correlation of geologic structures, and the collection of representative rock samples for the laboratory testing were accomplished. Laboratory strength data and rock mass characterization information were combined in order to obtain strength parameters for different failure scenarios. Once a simplified cross section of the volcano had been produced, strength values, earthquake loadings, and theorized pore pressures were inputted into a limit equilibrium stability program. The results show the crucial role that the highly fractured dacite domes in the northern portion of the volcano have in determining failure direction, and nature of the collapse.
DE: 5194 Instruments and techniques
DE: 5199 General or miscellaneous
DE: 5460 Physical properties of materials
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting