Evaluation of Development of the Mitchell Creek Landslide, B.C., using Remote Sensing, Geomorphological Analysis and Numerical Modelling

Abstract:

The Mitchell Creek Landslide of northwestern British Columbia is a large structurally controlled bedrock instability, with an estimated volume of 75 Mm³. It has developed over the last 60 years in response to rapid deglaciation, offering insight into changing conditions at juvenile rock landslides. The landslide is located in altered volcanic & volcaniclastic rocks of the Stikine Terrane at the intersection of two major regional faults. Multiple failure mechanisms have been identified over the 0.8 km² landslide area including toppling along steep foliation in the lower landslide and sliding along a well-defined rupture surface in the upper landslide. Geomorphological and engineering geological assessments have been completed at the site to characterize landslide properties and behaviour. Historic aerial photographs have been used to observe changes to the slope since 1956 and have captured the onset of surface deformation. Mapping of morphological and deformation features were undertaken on imagery from 1956, 1972, 1992, and 2010 to evaluate slope processes, failure mechanisms, and damage accumulation within the slope. Natural targets were also used to estimate landslide displacements over the past 60 years. Annual movement rates have been estimated to range from 0.1 to 0.8 m/yr over the landslide area. Displacement rates have been compared with historic glacial levels in the valley and modern environmental monitoring. A reconstruction of pre-failure geometry of the landslide was created from displacement estimates and structural geologic information. Rock mass properties and discontinuity orientations have been assessed from geotechnical investigations carried out between 2008 and 2013. A conceptual model of landslide behaviour and evolution has been developed and evaluated using both continuum and discontinuum numerical modeling techniques.