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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2018-272
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2018-272
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 21 Dec 2018

Research article | 21 Dec 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Mountain permafrost degradation documented through a network of permanent electrical resistivity tomography sites

Coline Mollaret1, Christin Hilbich1, Cécile Pellet1, Adrian Flores-Orozco2, Reynald Delaloye1, and Christian Hauck1 Coline Mollaret et al.
  • 1Department of Geosciences, University of Fribourg, Switzerland
  • 2Department of Geodesy and Geoinformation, TU Wien, Austria

Abstract. Mountain permafrost is sensitive to climate change and is expected to gradually degrade in response to the ongoing atmospheric warming trend. Long-term monitoring the permafrost thermal state is a key task, but it is problematic where temperatures are close to 0°C. The energy exchange is indeed often dominantly related to latent heat effects associated with phase change (ice/water), rather than ground warming or cooling. Consequently, it is difficult to detect significant spatio-temporal variations of ground properties (e.g. ice-water ratio) that occur during the freezing/thawing process with point scale temperature monitoring alone. Hence, electrical methods have become popular in permafrost investigations as the resistivities of ice and water differ by several orders of magnitude, theoretically allowing a clear distinction between frozen and unfrozen ground. In this study we present an assessment of mountain permafrost evolution using long-term electrical resistivity tomography monitoring (ERTM) from a network of permanent sites in the Central Alps. The time series consist of more than 1000 data sets from six sites, where resistivities have been measured on a regular basis for up to twenty years. We identify systematic sources of error and apply automatic filtering procedures during data processing. In order to constrain the interpretation of the results, we analyse inversion results and long-term resistivity changes in comparison with existing borehole temperature time series. Our results show that the resistivity data set provides the most valuable insights at the melting point. A prominent permafrost degradation trend is evident for the longest time series (19 years), but also detectable for shorter time series (about a decade) at most sites. In spite of the wide range of morphological, climatological and geological differences between the sites, the observed inter-annual resistivity changes and long-term tendencies are similar for all sites of the network.

Coline Mollaret et al.
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Short summary
We present a long-term multi-site electrical resistivity tomography monitoring network (more than 1000 datasets recorded from six mountain permafrost sites). Despite harsh and remote measurement conditions, the datasets are of good quality and show consistent spatio-temporal variations yielding significant added value to point-scale borehole information. Observed long-term trends are similar for all permafrost sites, showing ongoing permafrost thaw and ground ice loss due to climatic conditions.
We present a long-term multi-site electrical resistivity tomography monitoring network (more...
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