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

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.

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 et al. 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 ≥10^4.5Ωm (∼−0.5 °C), indicating frozen rock, displaying a core section with resistivities ≥10^4.7Ωm (∼−2 °C) (Krautblatter et al., 2010). We can differentiate seasonal variability, seen by laterally aggrading and degrading marginal sections (Krautblatter et al., 2010) and singular effects due to environmental factors and extreme weather events.

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.

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.

 

Krautblatter, M., Verleysdonk, S., Flores-Orozco, A. & Kemna, A. (2010): Temperature- calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography (Zugspitze, German/Austrian Alps). J. Geophys. Res. 115: F02003.

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. J. Geophys. Res. Earth Surf., 120, 745-762.