Hazard Assessment of Unstable and Potential Unstable Rock Slopes in Storfjord (Western Norway)

Abstract

To perform quantitative hazard assessments of unstable rock slopes based on magnitude-frequency relations detailed information about the specific unstable rock slopes is needed. Systematic field mapping in the Storfjord area in western Norway led to an inventory of 13 unstable rock slopes and 31 potential rock slopes. This study presents necessary input data for such assessment, namely volume estimates using the sloping local base level technique and a qualitative hazard ranking based on the hazard and risk classification system for unstable rock slopes in Norway. This hazard ranking is based on a series of geomorphological and structural criteria and signs of activity. The hazard ranking shows clearly different cumulative frequency distributions for unstable rock slopes and potential ones with average scores of 5.2 and 3.4, respectively, out of 12 maximum points. These differences are explained by the insufficient development of delimiting structures in potential unstable rock slopes due to the absence of past displacements.