Mapping, Hazard and Consequence Analyses for Unstable Rock Slopes in Norway

Systematic mapping for unstable rock slopes that can cause catastrophic failures has been carried out in Norway for 15 years. In this time a systematic mapping approach was developed that includes a hazard and a consequence analysis. The first weighs morphological signs of rock slope deformation, structurally based stability considerations, the state of slope activity and past events to come up with a hazard score. The second includes the analysis of the volume, the potential run-out area and if applicable the assessment of related displacement waves in case that the failure hits a water body or the assessment of the landslide dam in case that the failure would dam a valley. The goal of the consequence assessment is to assess the potential loss of life for possible failure scenarios. The hazard and consequence analyses are used by the Norwegian Water and energy Directorate to define high risk sites and for hazard zoning in relation to the Norwegian building codes. So far, 523 unstable rock slopes have been found, of which 110 were hazard and risk classified. 48 of the slopes have hazard zones that restrict building activities and 7 sites have been defined as high risk sites that are today under continuous surveillance.