Abstract

A conspicuous, linear scarp crosses an alpine ridge at Mt. Currie, British Columbia. Previous studies have shown that the northeast end of the scarp, which is up to 20 m high, is currently creeping, but the history and origin of the entire 1.6-km-long feature are unknown. An exploratory trench across an upslope-facing portion of the bedrock scarp and the adjacent sediment catchment revealed evidence for a minimum of three to four periods of activity dating from late Pleistocene to late Holocene time. Movement has occurred along near-vertical, gouge-filled shear zones, which represent pre-existing planes of weakness. These zones explain the continuity and linearity of the scarp. Warped and tilted sediments and a scarp-derived colluvial wedge provide evidence for the style of deformation, and are similar to structures and deposits of both gravitational spreading features (sackungen) and tectonic faults. The Mt. Currie scarp is more likely caused by gravitational forces, and is not a recently active tectonic fault, as has been previously suggested. The scarp's geometry and position in the landscape are compatible with gravitational failure. Slickenside striations in clay gouge from our trench show a displacement vector consistent with documented creep. The orientation of the scarp is not favorable for tectonic displacement, based on an evaluation of the regional seismogenic deformation field from earthquake P and T axes.

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