New multi-phase thermo-geophysical model: Validate ERT-monitoring & assess permafrost evolution in alpine rock walls (Zugspitze, German/Austrian Alps)

Abstract

<p><span>In the context of climate change, permafrost degradation is a key variable in understanding rock slope failures in high mountain areas. Permafrost degradation imposes a variety of environmental, economic and humanitarian impacts on infrastructure and people in high mountain areas. Therefore, new high-quality monitoring and modelling strategies are needed.</span></p><p><span>Electrical Resistivity Tomography (ERT) is the predominant permafrost monitoring technique in high mountain areas. Its high temperature sensitivity for frozen vs. unfrozen conditions, combined with the resistivity-temperature laboratory calibration on Wettersteinkalk (Zugspitze) (Krautblatter et al. 2010) gives us quantitative information on site-specific rock wall temperatures (Magnin <em>et al.</em> 2015). Long-term ERT-Measurements (2007/2014 – now) were taken at the Kammstollen along the northern Zugspitze rock face. Two high-resistivity bodies along the investigation area reach resistivity values ≥10<sup>4.5</sup></span>Ω<span>m (</span><span>∼</span><span>−0.5 </span><span>°</span><span>C), indicating frozen rock, displaying a core section with resistivities ≥10<sup>4.7</sup></span>Ω<span>m (</span><span>∼</span><span>−2 </span><span>°</span><span>C) (Krautblatter <em>et al.</em>, 2010). We can differentiate seasonal variability, seen by laterally aggrading and degrading marginal sections (Krautblatter <em>et al.</em>, 2010) and singular effects due to environmental factors and extreme weather events.</span></p><p><span>Here, we present a new local high-resolution numerical, process-orientated thermo-geophysical model (TGM) for steep permafrost rock walls. The model links apparent resistivities, the ground thermal regime and meteorological forcings as seasonality and long-term climate change to validate the ERT and project future conditions. The TGM comprises a surface energy balance model, conductive energy transport, turbulent and seasonal heat fluxes (sensible, latent, melt and rain heat fluxes) including phase-change, as well as a multi-phase rock wall composition.</span></p><p><span>Finally, we can reproduce the natural temperature field in the rock wall, assess the spatial-temporal permafrost evolution in alpine rock walls, validate the ERT measurements via the new TGM and the applicability of the laboratory derived resistivity-temperature relationship by Krautblatter et al. (2010) for natural rock-wall conditions.</span></p><p><span> </span></p><p><span>Krautblatter, M., Verleysdonk, S., Flores-Orozco, A. & Kemna, A. (2010): Temperature- calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity </span><span>tomography</span><span> (Zugspitze, German/Austrian Alps). <em>J. Geophys. Res. </em>115: F02003.</span></p><p><span>Magnin, F., Krautblatter, M., Deline, P., Ravanel, L., Malet, E., Bevington, A. (2015): Determination of warm, sensitive permafrost areas in near-vertical rockwalls and evaluation of distributed models by electrical resistivity tomography. <em>J. Geophys. Res. Earth Surf.</em>, 120, 745-762.</span></p>