Landslides in bedrock

Abstract Landslides in bedrock include some of the most common (rockfalls) and most destructive (rock avalanches) slope processes. The characteristic volumes, velocities, runout distances and frequencies of bedrock mass movement types can vary over many orders of magnitude. An understanding of the multiple attributes, contributing factors and processes is required to conduct a comprehensive hazard characterisation of bedrock landslides. The characterisation includes the mechanical properties of intact rock, orientation and surface characteristics of discontinuities, geologic history of the rock mass, climate and topography of the slope and any past and currently active tectonic and geomorphic processes. Rock-slope stability conditions can be divided into three broad categories based on the factor controlling them: rock structures, intact rock strength and rock mass strength. Applications of the progressive failure concept are presented to explain the behaviour of rock masses leading to a catastrophic slope failure. The range of bedrock mass movement types within the Varnes-based landslide classification scheme is also reviewed. Four cases studies – Seymareh (Iran), Mount Meager (Canada), La Clapiere (France) and Threatening Rock (United States) – are presented in detail to illustrate the range of bedrock landslide types and characteristics presented in this chapter. As with mass movements in other material types (snow, ice, soil and debris), inventory mapping, monitoring and modelling (numerical and physical) form the basis of bedrock landslide hazard recognition and anticipation. This chapter closes with a review of risk management strategies as applied to bedrock landslides. The individual components of the risk equation are presented along with examples of responses that could help reduce calculated risk. Avoidance is the simplest and most effective response to rock-slope instabilities as active mitigation is typically only effective for small-volume rockfalls and is only possible at significant economic cost for large slow-moving features.