Permafrost below the Timberline Confirmed and Characterized by Geoelectrical Resistivity Measurements, Bever Valley, Eastern Swiss Alps

Abstract

In the Bever Valley, Upper Engadine, eastern Swiss Alps, one‐dimensional DC resistivity soundings and two‐dimensional DC resistivity tomography were performed at a site where both GIS‐based modelling and measurements of the bottom temperature of the winter snow cover (BTS) suggest a potential permafrost occurrence at low altitude (1840 m ASL). The results of the geoelectric 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 expected at a low altitude location with permafrost temperatures probably close to 0 °C. The active layer appears to be fairly thin which is surprising for a permafrost occurrence at mean annual air temperatures well above 0 °C. Here, the reduced radiation due to the topography as well as the organic layers are considered to play an important role in insulating the subsurface and controlling the ground thermal regime. The permafrost occurrence 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 the organic layers provide good ground contact for the electrodes. Furthermore, the application of one‐dimensional DC resistivity soundings in combination with two‐dimensional DC resistivity tomography proves to be a useful tool for mapping and characterizing isolated permafrost occurrences on a small scale. Copyright © 2000 John Wiley & Sons, Ltd.