A Comparison of Frequency Domain Electro-Magnetometry, Electrical Resistivity Tomography and Borehole Temperatures to Assess the Presence of Ice in a Rock Glacier

Abstract

Alpine permafrost is currently warming, leading to changes such as active layer deepening and talik formation. Frequency domain electro-magnetometry (FDEM) measurements were tested as a simple and efficient method to investigate ground characteristics along two transects on the ice-rich Schafberg rock glacier in the Eastern Swiss Alps. The results were compared with electrical resistivity tomography (ERT) and ground temperature data acquired simultaneously in boreholes. FDEM provides information on the electrical properties of the ground, allowing to investigate ground-ice distribution. Our device allowed measurements to a depth of around 7 m. In ice-rich permafrost, FDEM can provide an approximation of the active layer thickness, and ice-free zones within the permafrost such as intra-permafrost taliks can be identified. This rapidly applicable geophysical method can be used to monitor ground ice distribution easily and efficiently, making it an ideal complement to borehole temperature data, which only provide point information and are costly to install and maintain. At the Schafberg site the three methods FDEM, electrical resistivity tomography and borehole temperature measurements provided similar results, with regard to active layer thickness and the presence of unfrozen zones within the ice-rich permafrost.

Changes in Ground Temperature and Dynamics in Mountain Permafrost in the Swiss Alps

“…In the beginning of 2019 a second talik started to form at 6.7 m depth and one appears to be forming at 11.2 m depth. The presence of taliks was confirmed by frequency domain electromagnometry measurements carried out in summer 2019 (Boaga et al, 2020). According to TLS data, only small signs of subsidence are visible directly at the borehole, but a stronger loss in surface height is occurring in the wider surroundings and the entire rock glacier shows a negative volume balance according to TLS measurements (Noetzli and Phillips, 2019).…”

“…Rising ground temperatures (Biskaborn et al, 2019;PERMOS, 2019), active layer thickening, varying ice-and water contents (Mollaret et al, 2019) and strongly increasing rock glacier deformation rates (PERMOS, 2019) have been observed in the (Swiss) Alps during the last two decades and are attributed to climate warming. Recent intra-permafrost talik formation in some rock glaciers (Zenklusen Mutter and Phillips, 2012b;Boaga et al, 2020) signal the onset of permafrost degradation. Induced by climate warming, higher water contents contribute to the acceleration of rock glaciers (Wirz et al, 2016;Buchli et al, 2018;Cicoira et al, 2019b).…”

Permafrost Biases Climate Signals in δ18Otree-ring Series from a Sub-Alpine Tree Stand in Val Bever/Switzerland

“…At lower altitudes (~1800 m asl) on the north-facing slope, geophysical soundings and ground surface measurements confirmed the occurrence of thin isolated, sporadic At lower altitudes (~1800 m asl) on the north-facing slope, geophysical soundings and ground surface measurements confirmed the occurrence of thin isolated, sporadic permafrost lenses at shallow depth down to~20 m [59,60,[73][74][75][76][77] (Figure 2B). Compared to permafrost sites in the periglacial zone (e.g., [78][79][80]), the active layer thickness is relatively shallow (1-3 m) and ground temperatures are just below zero degrees (−0.2 • C at 8 m depth). This subalpine permafrost occurrence is approximately 500 m below the expected lower limit of discontinuous permafrost, frequently represented by rock glaciers at 2300 m asl in the Upper Engadin [57,77,81,82].…”

Brief communication: Combining borehole temperature, borehole piezometer and cross-borehole electrical resistivity tomography measurements to investigate changes in ice-rich mountain permafrost

“…A widespread acceleration of ice-rich rock glaciers is being recorded in the Alps (Permos, 2019), increasing the likelihood of 20 mass movements such as debris flows from their frontal lobes in steep terrain connected to streams (Kummert and Delaloye, 2018). The acceleration has been attributed to ice warming induced by global warming and to rising water contents within the ice-rich permafrost (Cicoira et al, 2019). Ice and water contents of rock glaciers have been modelled to investigate future water availability (Pruessner et al, 2022), and the water-related dynamics of rock glaciers have been investigated based on aerial photography, in-situ GNSS and meteorological data (Wirz et al, 2016), as well as snow cover timing (Kenner et al, 25 2019).…”