Open Conference Systems, Nordic Geographers Meeting 2011

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A framework and tools for landslide risk assessment in the Faroe Islands
Mads-Peter J Dahl, Lis E Mortensen, Niels H Jensen, Anita Veihe

Last modified: 2011-02-11

Abstract


The Faroe Islands in the North Atlantic Ocean are highly susceptible to rainfall-induced landslides. Steep mountains and high precipitation favor the initiation of shallow slope failures in thin colluvial soil covering impermeable parent material. Following several landslide incidents in recent years, a research project has been initiated by the Faroese Earth and Energy Directorate to assess landslide risk in the Faroe Islands. In this presentation the general long term risk assessment framework is outlined, and the development of some risk assessment tools are shown. Landslide risk assessment in the Faroe Islands includes evaluation of landslide susceptibility, hazard, consequence and risk. Susceptibility and hazard describe the spatial and spatial-temporal probability of landslide occurrence, while risk is a product of hazard and societal consequence. When landslide risk, in terms of potential worth of loss within a reference time frame has been quantified, various risk-lowering mitigation measures can be considered. Debris flows and debris avalanches are the flow-type landslides constituting the greatest landslide threat in the Faroe Islands. Both phenomena are mainly initiated as debris slides. As a tool for the risk assessment project, a current study aims at quantifying debris slide magnitude and temporal occurrence as well as identifying preparatory factors responsible for spatial debris slide distribution in the Faroese landscape. In the study a multi-temporal landslide inventory in a 159 km2 study area is compiled from aerial photo interpretation, fieldwork and anecdotal sources. A magnitude cumulative-frequency relationship of the 219 debris slides shows that frequencies of slope failures above 100 m2 can be predicted from the power-law function: y=788.5x-1.25, r2=0.98. Preparatory factors responsible for spatial debris slide distribution are quantified through GIS-supported Discriminant Function Analysis. Nine geological, geomorphological and land use factors are included in the multivariate analysis. Final results of the study will serve as important contributions in the process to quantify debris flow and debris avalanche risk in the Faroe Islands.