Identifying mountain permafrost degradation by repeating historical ERT-measurements

Abstract

Abstract. Ongoing global warming intensifies the degradation of mountainous permafrost. Permafrost thawing impacts landform evolution, reduces fresh water resources, enhances the potential of natural hazards, and thus has significant socio-economic impact. Electrical resistivity tomography (ERT) has been widely used to map the ice-containing permafrost by its resistivity contrast compared to the surrounding non-frozen medium. This study aims to reveal the effects of ongoing climate warming on alpine permafrost by repeating historical ERT and analysing the temporal changes in the resistivity distribution. In order to facilitate the measurements, we introduce and discuss the employment of textile electrodes. These newly developed electrodes significantly reduce working effort, are easy to deploy on blocky surfaces, and yield sufficiently low contact resistances. We analyse permafrost evolution on three periglacial landforms (two rock glaciers and one talus slope) in the Swiss and Austrian Alps by repeating historical surveys after periods of 10, 12, and 16 years, respectively. The resistivity values have been significantly reduced in ice-poor permafrost landforms at all study sites. Interestingly, resistivity values related to ice-rich permafrost in the studied active rock glacier partly increased during the studied time period. To explain this apparently counterintuitive (in view of increased resistivity) observation, geomorphological circumstances such as the relief and increased creeping velocity of the active rock glacier, are discussed by using additional remote sensing data. The present study highlights ice-poor permafrost degradation in the Alps resulting from ever-accelerating global warming.

The summer heatwave in 2022 and its role in changing permafrost and periglacial conditions at a historic mountain pass in the Eastern Alps (Hochtor, Hohe Tauern Range, Austria)

“…Drawbacks in repeating previous ERT surveys could be different measurement devices used during the initial and the repeated campaign or finding again the initial course of a profile or even the position of the individual electrodes (commonly the steel rods). Buckel et al 61 repeated ‘historical’ ERT surveys after periods of 10 to 16 years in the Swiss and Austrian Alps. The accuracy of their historical and more recent measured location data is within the range of a standard GPS device, which is 5–10 m horizontally 61 .…”

“…Buckel et al 61 repeated ‘historical’ ERT surveys after periods of 10 to 16 years in the Swiss and Austrian Alps. The accuracy of their historical and more recent measured location data is within the range of a standard GPS device, which is 5–10 m horizontally 61 . Furthermore, finding the location of historical ERT profiles might be accomplished by refinding distinct boulders visible in earlier orthophotographs or other sources 61 .…”

“…As judged from field‐based measurements at a nearby site (surface velocity rates of 3.5 cm/year 26 ), we can assume a maximum relative misplacement of individual electrode positions between 2019 and 2022 in the order of a maximum of 10 cm. This minor change in the position is considered irrelevant if compared to, for instance, those of active rock glaciers 61 …”

“…The accuracy of their historical and more recent measured location data is within the range of a standard GPS device, which is 5-10 m horizontally. 61 Furthermore, finding the location of historical ERT profiles might be accomplished by refinding distinct boulders visible in earlier orthophotographs or other sources. 61 In our study, we were able to exclude the problem of localising the initial profiles or because of the usage of different instruments in a further field campaign.…”

“…61 Furthermore, finding the location of historical ERT profiles might be accomplished by refinding distinct boulders visible in earlier orthophotographs or other sources. 61 In our study, we were able to exclude the problem of localising the initial profiles or because of the usage of different instruments in a further field campaign. 59 We carried out our ERT measurements in both years at the same profiles (based on the GNSS data), with the same device (Geotom-2D System) and with the same set-up (4 m spacing, 25 spike electrodes).…”