Abstract
Spectral induced polarization (SIP) measurements were collected at the Lapires talus slope, a long-term permafrost monitoring site located in the Western Swiss Alps, to assess the potential of the frequency dependence (within the frequency range of 0.1–225 Hz) of the electrical polarization response of frozen rocks for an improved permafrost characterization. The aim of our investigation was to (a) find a field protocol that provides SIP imaging data sets less affected by electromagnetic coupling and easy to deploy in rough terrains, (b) cover the spatial extent of the local permafrost distribution, and (c) evaluate the potential of the spectral data to discriminate between different substrates and spatial variations in the volumetric ice content within the talus slope. To qualitatively assess data uncertainty, we analyze the misfit between normal and reciprocal (N&R) measurements collected for all profiles and frequencies. A comparison between different cable setups reveals the lowest N&R misfits for coaxial cables and the possibility to collect high-quality SIP data in the range between 0.1–75 Hz. We observe an overall smaller spatial extent of the ice-rich permafrost body compared to its assumed distribution from previous studies. Our results further suggest that SIP data help to improve the discrimination between ice-rich permafrost and unfrozen bedrock in ambiguous cases based on their characteristic spectral behavior, with ice-rich areas showing a stronger polarization towards higher frequencies in agreement with the well-known spectral response of ice.
Highlights
Mountain permafrost regions are highly sensitive to climate changes, with significant implications for the hydrological regimes
Single multicore cables show a high number of normal and reciprocal (N&R) outliers for all 320 frequencies with a poor spatial consistency in the readings observed in the pseudosection
Even for 75 Hz, there are still 172 of 711 N&R pairs remaining for single coaxial cables after filtering, whereas for separated multicore cables only 7 of 351 N&R pairs remained after filtering
Summary
Mountain permafrost regions are highly sensitive to climate changes, with significant implications for the hydrological regimes. Water reservoirs and sources in many mountain ranges in the world are threatened by changes of the cryosphere; and knowledge of the ground ice and water content in permafrost regions is critical for the estimation of water storage 25 capacities and future water supplies (e.g., Arenson and Jakob, 2010; Halla et al, 2021; Harrington et al, 2018; Langston et al, 2011; Rangecroft et al, 2016; Schrott, 1998). From borehole temperature monitoring alone we cannot differentiate 30 between unfrozen and frozen water content, as we can observe water in the liquid phase even at negative temperatures
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