HR: 1340h
AN: V43B-1425    [Abstracts]
TI: Slope Failure on Subglacial Volcanoes: Effects of Lithification, Fluid Pressure, and Seismic Loading on Edifice Stability
AU: * Neuffer, D P
EM: neufferd@mines.unr.edu
AF: Geological Engineering Program, Dept. of Geological Sciences and Engineering, Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, NV 89557-0138 United States
AU: Schultz, R A
EM: schultz@mines.unr.edu
AF: Geological Engineering Program, Dept. of Geological Sciences and Engineering, Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, NV 89557-0138 United States
AU: Watters, R J
EM: watters@mines.unr.edu
AF: Geological Engineering Program, Dept. of Geological Sciences and Engineering, Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, NV 89557-0138 United States
AB: Large-scale paleolandslides are commonly observed on subglacial volcanoes. Rapid drainage of the surrounding englacial lake, removal of buttressing ice, and hydrothermal alteration are often cited as possible causes for slope failure on subglacial volcanoes. Limit-equilibrium slope stability analyses show that the failure of unlithified slopes during rapid drawdown of the englacial lake is the most likely mechanism for landsliding on a subglacial volcano in the Wells Gray-Clearwater Volcanic Field, British Columbia. Our modeling suggests that large-scale slope instability on subglacial volcanoes most likely requires slope materials that are not completely lithified along with rapid drainage of surrounding water. Pyramid Mountain is a 240 m high subglacial volcano in Wells Gray Provincial Park in central British Columbia, Canada. Geomechanical characterization of hyaloclastite outcrops and landslide mapping were performed in the field. The failure conditions of a prominent landslide on the east flank of the mountain were modeled in SLIDE. In the first scenario, the strength of the current, lithified rock mass was used to test slope stability. The second scenario evaluated the stability of cohesionless, unlithified deposits for a range of possible frictional strengths. For both scenarios, hydrologic conditions were varied iteratively from a fully saturated slope, simulating rapid and complete drawdown of surrounding water, to a dry slope. Results show that rapid drawdown of the englacial lake with simultaneous 0.4 g horizontal ground acceleration would be necessary to cause the rock slope in the first scenario to fail, an unlikely event. In contrast, for the second scenario, rapid drawdown of the lake alone causes the east flank to fail for friction angles ranging from 30-58 degrees. Rapid drawdown is necessary for failure of unlithified deposits below seismic loads of 0.2 g. Hence, edifice failure on subglacial volcanoes probably occurs early, as the englacial lake is draining and before the hyaloclastite has dewatered and lithified.
DE: 8499 General or miscellaneous
DE: 8045 Role of fluids
DE: 1827 Glaciology (1863)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting