Approach for systematic rockslide mapping of unstable rock slopes in Norway

Abstract

Systematic mapping of unstable rock slopes has been carried out in Norway since 2005. More than 300 unstable or potential unstable rock slopes have been detected and characterized so far. This utilises a standardized hazard and risk classification system that was established in 2012. The determination of the hazard and risk level follows a new standard approach for the systematic mapping of the analyzed sites that is iterative, starting with simple assessments. However the higher the hazard/risk level of a site is, the larger the amount of geological information collected, and the more detailed the run-out models and consequence analyses that will be carried out. This approach allows mapping resources to be focused on sites with higher risk level, delivering products with different levels of detail. Rock slope failures that would not result in any loss of life, as there is no life line or building in the run-out area, are mapped without a probability assessment. These analyses thus have no scale for the hazard class. Rock slope failures that can result in loss of life are analyzed using qualitative hazard analyses, thus the mapping products are hazard maps with qualitative probability classes. The work on this mapping approach is still ongoing; methods for assessment of the occurrence and consequences of secondary processes (e.g., triggering of displacement waves in water bodies, river damming and outburst floods) need still to be defined. An iterative approach will also be developed to analyze those processes.