Rock slope failures along the Forkastningsfjellet coastline, Svalbard: characteristics and implications for controlling and triggering factors

Climate warming and the related permafrost degradation are thought to influence slope stability, landscape evolution, and the natural hazard potential in polar- and high mountain regions. In this context, we investigate the coastal range of Forkastningsfjellet, Svalbard, which is affected by rock slope deformations of different magnitudes and age. Based on a detailed multidisciplinary investigation, we discuss the causes, kinematics and timing of rock slide activity. The distinct stair-stepped morphostructural relief of the Forkastningsfjellet ridge is the result of a giant postglacial deep-seated rock slide, which involved a minimum rock mass volume of 0.10 km³ and was probably related to the deglaciation of Isfjorden. Rock failure and movement in the hanging wall of a NW-dipping listric sliding surface led to the fragmentation of the sliding mass into separated tilt blocks. Since then mass wasting and seacliff erosion take place along the steep slopes of the coastal tilt blocks and on August 16th 2016 a coastal block of the postglacial Forkastningsfjellet rock slide was affected by a rotational rock slide comprising a volume of 175,000m³. As the reactivation of individual slide blocks could have severe consequences for the coastal regions of Longyearbyen by related displacement waves, a back analysis was carried out to derive potential controlling and triggering factors of the recent slope failure. Although the analysis suggests a structural control on the type and mechanism of slope failure, a significant impact of climate-related factors like permafrost degradation and increasing availability of water has to be considered.