A simple qualitative approach for mapping regional landslide susceptibility in the Faroe Islands

M.-P J Dahl,A Veihe,N H Jensen,L E Mortensen

doi:10.5194/nhess-10-159-2010

Abstract

Abstract. The Faroe Islands in the North Atlantic Ocean are highly susceptible to landslides. Following recent landslide incidents, Jarðfeingi (Faroese Earth and Energy Directorate) has pointed out, that the risk of human lives or of property being lost or affected by landslides may be increasing. This paper aims at presenting and testing a simple qualitative approach for mapping regional landslide susceptibility in the Faroe Islands, using few key parameters. The susceptibility model holds information about both landslide initiation areas and runout zones. Landslide initiation areas are determined from slope angle thresholds (25°–40°) and soil cover data, while runout zones are delineated using the angle of reach approach taking into account the presence/absence of geological benches in the runout path, which has not been considered in earlier studies. Data input is obtained from a landslide database containing 67 debris flows throughout the Faroe Islands. Angle of reach values differ significantly with the presence/absence of geological benches in the runout path. Two values of angle of reach, 21.5° and 27.6°, are used for calculating runout zones. The landslide susceptibility model is tested in a study area at the town of Klaksvík in the northern part of the Faroe Islands. A map validation comparing predicted susceptibility zones with a validation-dataset of 87 actual landslides in the study area reveal that 69% and 92%, respectively, of actual landslide initiation areas and runout zones are correctly predicted. Moreover 87% of the actual landslides are included in the overall predicted landslide susceptibility areas.

Highlights

The Faroe Islands in the North Atlantic Ocean (Fig. 1) are highly susceptible to landslides
Landslide initiation areas are determined from slope angle thresholds (25◦–40◦) and soil cover data, while runout zones are delineated using the angle of reach approach taking into account the presence/absence of geological benches in the runout path, which has not been considered in earlier studies
Corominas (1996), plotting log landslide volume for rockfalls, earthflows and translational landslides against log landslide height (H )/horizontal landslide length (Lh), showed that notably rockfalls and debris flows with volumes

Summary

Introduction

The Faroe Islands in the North Atlantic Ocean (Fig. 1) are highly susceptible to landslides. Landslides are mainly rock falls and debris flows as defined by Cruden and Varnes (1996). The latter are very common (Dahl, 2007), due to steep landscape, high precipitation (900–3200 mm/yr), (Cappelen and Laursen, 1998), and basaltic parent material overlain by a colluvial soil layer ranging from 0 to 8 m (Dahl, 2007). During recent years damaging landslide events, mainly triggered by extreme rainfalls, have led to increased focus on loss of human lives and property caused by debris flows. There is a growing need for developing landslide susceptibility maps which may be used for planning purposes

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Conclusion