Mechanisms of slope failure in Valles Marineris, Mars and Wells Gray-Clearwater Volcanic Field, British Colombia

The trough system of Valles Marineris, Mars contains numerous landslides in basaltic wall rock and interior layered deposits (ILDs). Landslides were mapped in the ILDs and modeled along with wall rock failures using limit-equilibrium slope stability analysis. Wall rock landslides required superhydrostatic fluid pressures of at least 41% of overburden pressure or ground accelerations of at least 0.19 Mars g for failure. Ground shaking probably triggered most wall rock landslides. ILD landslides may be a result of gravitational, fluid, or seismic loading. Limit-equilibrium analyses also showed that landslides on Pyramid Mountain, a subglacial volcano in British Columbia, were probably triggered by the rapid drawdown of a surrounding englacial lake with no ground acceleration required. Prior to failure, Pyramid Mountain was at least partially lithified and significantly asymmetric in shape. Failures of lithified subglacial and subaqueous volcanic edifices may be triggered by rapid drawdown of surrounding water without seismic loading.