Abstract

On July 13, 2005 a complex 3 Mm3 and 1.5 km long rock slide-debris avalanche occurred near Sutherland River, 40 km west of Fort St. James, British Columbia, Canada. The landslide was initiated in a succession of sub-horizontal competent mafic basalts (Endako Formation) capping weaker felsic volcanic and volcaniclastic rocks (Ootsa Lake Group) of Eocene age. Several landslides have been observed in similar volcanic successions worldwide including in southern British Columbia. Some common characteristics of these landslides are: structurally undisturbed; horizontal to sub-horizontal bedding; curved head scarp; steep joints; debris consists of intact blocks; volcaniclastics containing smectite (expandable clay mineral); fossils and lignite within the volcaniclastics. The Sutherland landslide is one of many large landslides that have occurred in recent years in northern British Columbia. At least eight other large landslides have been triggered in volcanic rocks within the Nechako plateau.

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