Rock avalanches - distribution and frequencies in the inner part of Storfjorden, Møre og Romsdal County, Norway

NGU Rapport 2009.002

Past landslide deposits store valuable and important information that can be used for geohazard analysis. This includes data on frequency of events, run-out distances and dynamics of rock avalanches. Investigations of rock-avalanche events also give possibilities for back-calculation (modelling of avalanches), such as conditions for sliding in potential unstable slopes.

A complete swath bathymetry dataset from the inner parts of Storfjorden and its tributary fjords has been studied. Based on this dataset and seismic data, rock-avalanche deposits on the fjords bottom have been mapped. An inventory of avalanche debris distribution and volumes has been compiled. A relative chronostratigraphy is elaborated, and slides are tentatively put into this frame based on seismostratigraphic position and freshness of surface morphology. In many cases it is difficult to distinguish between large rock-avalanches with volumes more than 100000m3, and rock fall and alluvial cones. Hence the number of avalanches may be higher than listed in the inventory.