Abstract
Abstract. Climate-induced warming increasingly leads to degradation of high-alpine permafrost. In order to develop early warning systems for imminent slope destabilization, knowledge about hydrological flow processes in the subsurface is urgently needed. Due to the fast dynamics associated with slope failures, non- or minimally invasive methods are required for inexpensive and timely characterization and monitoring of potential failure sites to allow in-time responses. These requirements can potentially be met by geophysical methods usually applied in near-surface geophysical settings, such as electrical resistivity tomography (ERT), ground-penetrating radar (GPR), various seismic methods, and self-potential (SP) measurements. While ERT and GPR have their primary uses in detecting lithological subsurface structure and liquid water/ice content variations, SP measurements are sensitive to active water flow in the subsurface. Combined, these methods provide huge potential to monitor the dynamic hydrological evolution of permafrost systems. However, while conceptually simple, the technical application of the SP method in high-alpine mountain regions is challenging, especially if spatially resolved information is required. We here report on the design, construction, and testing phase of a multi-electrode SP measurement system aimed at characterizing surface runoff and meltwater flow on the Schilthorn, Bernese Alps, Switzerland. Design requirements for a year-round measurement system are discussed; the hardware and software of the constructed system, as well as test measurements are presented, including detailed quality-assessment studies. On-site noise measurements and one laboratory experiment on freezing and thawing characteristics of the SP electrodes provide supporting information. It was found that a detailed quality assessment of the measured data is important for such challenging field site operations, requiring adapted measurement schemes to allow for the extraction of robust data in light of an environment highly contaminated by anthropogenic and natural noise components. Finally, possible short- and long-term improvements to the system are discussed and recommendations for future installations are developed.
Highlights
Long-term borehole temperature records document the degradation of permafrost on a global scale (Biskaborn et al, 2019), which can release soil organic carbon into the atmosphere (e.g., Schuur et al, 2015) and negatively affect slope stability in alpine regions (e.g., Huggel et al, 2012)
While electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) have their primary uses in detecting lithological subsurface structure and liquid water/ice content variations, SP measurements are sensitive to active water flow in the subsurface
We here report on the design, construction, and testing phase of a multi-electrode SP measurement system aimed at characterizing surface runoff and meltwater flow on the Schilthorn, Bernese Alps, Switzerland
Summary
Long-term borehole temperature records document the degradation of permafrost on a global scale (Biskaborn et al, 2019), which can release soil organic carbon into the atmosphere (e.g., Schuur et al, 2015) and negatively affect slope stability in alpine regions (e.g., Huggel et al, 2012). Few applications of long-term SP monitoring setups for mountainous regions have been reported: Blake and Clarke (1999) report on multi-year SP measurements at the bottom of a glacier in Canada, finding clear evidence for electrical streaming potentials caused by periodic and episodic water movement at the bed of the glacier. Friedel et al (2004) present SP results from the Merapi volcano, finding evidence for periodic and episodic water movement caused by atmospheric changes and speculating about transients induced by volcanic activity Despite these promising studies, SP measurements in mountainous and permafrost regions remain relatively scarce (e.g., Hauck, 2013), possibly due to the problems and ambiguities arising in the analysis of SP data with regard to subsurface flow parameters in these complex environments. We finish with a short discussion on possible improvements and alternative approaches for future system designs
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