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.
Highlights
Ice-rich ground is common in alpine sediments above the treeline and often constitutes the lower limit of permafrost (Lerjen et al, 2003; Scapozza et al, 2011; Kenner and Magnusson 2017)
We present first results obtained in summer 2019 using hand-held frequency domain electromagnetometry (FDEM) on the ice-rich Schafberg rock glacier in the eastern Swiss Alps, and compare the results to data obtained simultaneously by borehole temperature logging and electrical resistivity tomography (ERT) measurements
We tested the use of frequency domain electro-magnetometry (FDEM) to assess ground ice distribution and (ALT) and compare results with data delivered by the electrical resistivity tomography (ERT) technique and borehole temperature measurements
Summary
Ice-rich ground is common in alpine sediments above the treeline and often constitutes the lower limit of permafrost (Lerjen et al, 2003; Scapozza et al, 2011; Kenner and Magnusson 2017). It is defined by the presence of excess ice, meaning that the ice content exceeds the total pore volume of the ground. Important changes in the ice to water ratio within the permafrost body, which mainly occur close to 0 °C, are not discernible from ground temperature data alone This makes the monitoring of ice-rich permafrost during phase change challenging (Kaab et al, 2007; Jones et al, 2018; Mollaret et al, 2019)
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