Permafrost below the timberline confirmed and characterized by geoelectrical resistivity measurements, Bever Valley, eastern Swiss Alps

In the Bever Valley, Upper Engadine, eastern Swiss Alps, one-dimensional DC resistivity soundings and two-dimensional DC resistivity tomography were p erformed at a site where both GIS-based modelling and measurements of the b ottom temperature of the winter snow cover (BTS) suggest a potential permaf rost occurrence at low altitude (1840 m ASL). The results of the geoelectri c measurements indeed point to a permafrost occurrence below the timberline which consists of several thin permafrost lenses. In comparison with other Alpine permafrost sites the resistivities are fairly low which might be ex pected at a low altitude location with permafrost temperatures probably clo se to 0 degreesC. The active layer appears to be fairly thin which is surpr ising for a permafrost occurrence at mean annual air temperatures well abov e 0 degreesC. Here, the reduced radiation due to the topography as well as the organic layers are considered to play an important role in insulating t he subsurface and controlling the ground thermal regime. The permafrost occ urrence is assumed to be a result of the interaction of climatic conditions and topography as well as surface and subsurface factors. The application of resistivity measurements is shown to be a useful geophysical method as t he organic layers provide good ground contact for the electrodes. Furthermo re, the application of one-dimensional DC resistivity soundings in combinat ion with two-dimensional DC resistivity tomography proves to be a useful to ol for mapping and characterizing isolated permafrost occurrences on a smal l scale. Copyright (C) 2000 John Wiley & Sons, Ltd.