Permafrost is disappearing at the Mount Zugspitze (D/A): challenges and results after 10 years of monthly geoelectrical measurements.

Alpine permafrost degradation boosted by climate change is recorded worldwide, posing a significant threat to slope stability. A comprehensive assessment of this risk necessitates continuous monitoring of the rate of permafrost changes, for example, with electrical resistivity tomography (ERT). Although ERT has been employed in more than 1000 studies worldwide to detect permafrost, only a few sites are monitored with high temporal resolution and present more than a decade of uninterrupted observations.

Whitin the Kammstollen tunnel (2750 m asl, Mount Zugspitze, DE/AT), geoelectrical tomographies of the north face have been conducted since 2007. In the last ten years, an extensive dataset has been collected monthly employing consistent procedures and permanent electrodes. Recently, we updated the inversion methods to the most recent standards, and after reprocessing old data, we precisely quantified the evolution of permafrost in the last decade. In line with the observed increase in air temperature, the permanently frozen area shows a gradual but consistent reduction during the summer months, with the record minimum value recorded at the end of summer 2023. This study highlights the limits of laboratory calibrations, especially in the presence of different degrees of rock fragmentation (fault zone). Further, we show the influence of error models on inversion results and on the quantification of resistivity changes, confirming the need for repeated estimation of measurement errors. 

The unique geoelectrical dataset here presented, bolstered by many simultaneous supplementary information, contributes to better defining the role of geoelectrical monitoring for understanding the thermal responses of alpine permafrost environments to present and future climate-change-induced stresses.