Preconditioning of mountain permafrost towards degradation detected by electrical resistivity

• Published in: Environmental Research Letters
• Main Authors: Hauck, Christian, Hilbich, Christin
• Other Authors: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, GCOS Switzerland, MeteoSwiss
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IOP Publishing 2024
• Subjects: Antarc*; Antarctica; Ice; permafrost
• Online Access: http://dx.doi.org/10.1088/1748-9326/ad3c55; https://iopscience.iop.org/article/10.1088/1748-9326/ad3c55; https://iopscience.iop.org/article/10.1088/1748-9326/ad3c55/pdf

Abstract Warming permafrost has been detected worldwide and is projected to continue during the next century by many modelling studies. In mountain regions, this can lead to potentially hazardous impacts on short time-scales by an increased tendency for slope instabilities. However, time scales of permafrost thaw and the role of the ice content are less clear, especially in heterogeneous mountain terrain, where ice content can vary between zero and supersaturated conditions over small distances. Warming of permafrost near the freezing point shows complex inter-annual behaviour due to latent heat effects during thawing and the influence of the snow-cover, which is governed by non-linear processes itself. 
We demonstrate a preconditioning effect within near-surface layers in mountain permafrost that causes non-linear degradation and accelerates thaw. We hypothesise that a summer heat wave, as seen e.g. in the Central European summers 2003, 2015 and 2022, will enhance permafrost degradation if active layer and top of permafrost layer are already preconditioned, i.e. have reduced latent heat content. This preconditioning can already be effectuated by a singular warm year, leading to exceptionally strong melting of ground ice. On sloping terrain this ice-loss can be considered as irreversible, as large parts of the melted water will drain during the process, and an equivalent build-up of ice in cold years does not happen on similar time-scales as the melting. We propose a simple geophysical approach based on electrical resistivity tomography (ERT) surveys that can assess the state of preconditioning in the absence of boreholes. In addition, we will show that resistivity data from a total of 124 permafrost sites in the Andes, Europe, and Antarctica adhere to a distinct power law behaviour between unfrozen and frozen state, which confirms the consistent electrical behaviour of permafrost and active layer material over a wide range of landforms and material composition.