Landsliding at Cement Creek, Kluane Ranges, Southwestern Yukon

A large block slide affecting an area of approximately 1.0 square km was reported to have occurred on Cement Creek Y.T. (115G/5) between February 15 and March 15, 1983. Landsliding is confined to basaltic andesites in the lower unit of the Wrangell Lavas. Hydrothermal alteration of flow-top breccias and the tilting of strata towards an open face bordering Cement Creek predispose rock to slip along bedding planes. Surveys conducted during June to August 1986 detected displacements of 10-12 cm during an 8 week period. Seismic refraction and electrical resistivity surveys conducted on the slide mass suggest that most ground failure was caused by strong ground motion during an initial episode of rapid displacement and that the rupture surface lies beneath the lower limit of permafrost. Ground-water accumulation on and above the rupture surface followed by landslide initiation during a burst of low magnitude seismicity is suggested as a slide mechanism.