Preliminary inventory of rock avalanche deposits and their related sources in Norway : Regional distribution, main features and topographic constraints

Abstract

In this report we have assessed some of the characteristics of the 248 rock avalanche deposits (rock slope failure deposits and their related source areas) inventoried in Norway up to date. These pre-historic and historic rock avalanche deposits are mostly located in the North (Troms and Finnmark counties) and in the South (Vestland and Møre og Romsdal counties) of Norway. Their spatial distribution is clearly correlated to relief conditions. The lithologies involved in the rock avalanche events in the North and the South differ, which can be related to different dominant lithologies in both regions. The identified deposits are present on land, in fjords and lakes, or a combination of those. Some are very well preserved, while others have been eroded by rivers or buried by fluvial deposits. Our work shows that the mobility of the rock avalanches is correlated to the slope conditions. A preliminary result is that mobility on average decreases with increasing slope angle. This relation, that has not been documented in previous studies, could be related to energy loss under particular topographic conditions in deeply glacially eroded valleys. While we investigate a significant number of past rock avalanche events in this report, systematic mapping at the national scale is likely to (i) shed light on the uncertainties identified in this report, (ii) provide data with the potential to improve the understanding of rock avalanche occurrence and dynamics, and (iii) generate baseline data for improved assessment of run-out length of future rock avalanche scenarios.