Hazard assessment of potential periglacial debris flows based on GIS-based spatial modelling and geophysical field surveys: a case study in the Swiss Alps

Abstract

Combined geomorphological and geophysical approaches were used to perform a hazard assessment of potential periglacial debris flow. Possible debris flow initiation zones were identified within a GIS-based model and located based on geomorphic attributes which contribute the most to this type of instability. In permafrost-affected alpine environments, these include the extent and location of ground ice and permafrost. In a potential debris flow-starting zone in the Upper Engadine (moraine/debris rock glacier complex Boval) two-dimensional electrical resistivity surveys were used to detect the presence/absence of permafrost and to estimate active-layer depth. The results show that the moraine complex represents a periglacial debris reservoir which consists of frozen and unfrozen debris. The ice-bonded part of the moraine is largely protected from sudden destabilisation and retrogressive erosion can be assumed to be limited. However, future degradation or loss of permafrost in the lower parts of the debris rock glacier would increase the amount of erodible debris and generally reduce mechanical stability.