Temperature‐calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography (Zugspitze, German/Austrian Alps)

Abstract

[1] Changes of rock and ice temperature inside permafrost rock walls crucially affect their stability. Permafrost rocks at the Zugspitze were involved in a 0.3-0.4 km 3 rockfall at 3.7 ka B.P. whose deposits are now inhabited by several thousands of people. A 107 year climate record at the summit (2962 m asl) shows a sharp temperature increase in 1991-2007. This article applies electrical resistivity tomography (ERT) to gain insight into spatial thaw and refreezing behavior of permafrost rocks and presents the first approach to calibrating ERT with frozen rock temperature. High-resolution ERT was conducted in the north face adjacent to the Zugspitze rockfall scarp in February and monthly from May to October 2007. A smoothness-constrained inversion is employed with an incorporated data error model, calibrated on the basis of normal reciprocal measurement discrepancy. Laboratory analysis of Zugspitze limestone indicates a bilinear temperature-resistivity relationship divided by a 0.5 ± 0.1°C and 30 ± 3 kWm equilibrium freezing point and a twentyfold increase of the frozen temperature-resistivity gradient (19.3 ± 2.1 kWm/°C). Temperature dominates resistivity changes in rock below −0.5°C, while in this case geological parameters are less important. ERT shows recession and readvance of frozen conditions in rock correspondingly to temperature data. Maximum resistivity changes in depths up to 27 m coincide with maximum measured water flow in fractures in May. Here we show that laboratory-calibrated ERT does not only identify frozen and unfrozen rock but provides quantitative information on frozen rock temperature relevant for stability considerations.Citation: Krautblatter, M., S. Verleysdonk, A. Flores-Orozco, and A. Kemna (2010), Temperature-calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography (Zugspitze, German/Austrian Alps),

Evidence of frost-cracking inferred from acoustic emissions in a high-alpine rock-wall

“…However, in the field, such conditions are never achieved and it may be difficult to robustly distinguish the role of volumetric expansion (as water turns into ice) from that of ice segregation. A number of factors such as solutes, pressure, pore size and pore material can depress the freezing point of water contained in rock (Krautblatter et al, 2010) as in any porous media, is progressive (Coussy and Fen-Chong, 2005) occurring over a whole range of sub-zero temperatures. Volumetric expansion-induced damage could potentially occur over this whole range of temperatures.…”

A spatial and temporal analysis of different periglacial materials by using geoelectrical, seismic and borehole temperature data at Murtèl–Corvatsch, Upper Engadin, Swiss Alps

“…Delaloye and Lambiel, 2005;Lambiel and Pieracci, 2008;Morard, 2011). Knowing the geophysical properties of periglacial material provides insight into thermal and hydrological processes such as spatial thaw and refreezing processes of permafrost rocks (Krautblatter et al, 2010) or enables the identification of water migration processes within landslide areas (Marescot et al, 2008). In addition, the geotechnical stability of thawing permafrost slopes partly depends on the same physical properties and their changes in time, leading to instabilities of engineering structures such as cable car pylons or avalanche protection structures (Phillips et al, 2007).…”

“…The ERT-monitoring (ERTM) technique has become an appropriate technique for observing temporal changes in the active layer, and has already been successfully applied within the last years (Hauck, 2002;Kneisel, 2006;Krautblatter et al, 2010;Ottowitz et al, 2011;Hilbich et al, 2011). In the year 2005, the first installation of a fixed ERTM network in permafrost was undertaken at different mountain permafrost sites in the Swiss Alps by the Swiss Permafrost Monitoring Network (PER-MOS; Hilbich et al, 2008a).…”

“…The abovementioned studies are based on a qualitative interpretation of the ERT results for permafrost distribution; further steps would be a quantitative interpretation, for example for providing the percentage amount of ice and its changes in time. First approaches are given by Krautblatter et al (2010), who interpreted temperature and stability relevant factors by calibrating ERT with frozen rock temperatures, and by Hauck et al (2011), who used a four-phase model to calculate the volumetric fractions of the ground constituents.…”

P-wave velocity changes in freezing hard low-porosity rocks: a laboratory-based time-average model

“…Alpine rock cliffs in permafrost regions mostly consist of hard lowporosity rocks (< 10 %), according to Tiab and Donaldson's (2004) definition, and the applicability of electrical and seismic methods to these is yet unclear. While the relationship between electrical resistivity and frozen low-porosity bedrock has been investigated by Krautblatter et al (2010), this article will focus on the applicability of p-wave refraction seismics to low-porosity bedrock.…”