A better understanding of current mountain permafrost degradation implies a temporal and spatial permafrost distribution monitoring. Geophysical methods are widely used to explore the subsurface, as they are cost-efficient and do not disturb the ground. In this project, Electrical Resistivity Tomography (ERT) and Refraction Seismic Tomography (RST) are jointly used to investigate mountain permafrost at several sites in Switzerland but also at other permafrost sites worldwide. These two methods are chosen, because electrical resistivity and P-wave velocity discriminate between ice, water and air cavities by several orders of magnitude.

Borehole temperature record and geophysical measurements are hereby complementary data, as ground temperatures give no information about ice contents. The ice and water contents are estimated from the geophysical measurements through the so-called four-phase-model (Hauck et al., 2011). A long-term geophysical monitoring, ideally in automated and continuous mode (see Hilbich et al. 2011, for ERT monitoring), is essential to interpret current and future mountain cryosphere evolution. 

Duration: 2015-2019

Funded by: University of Fribourg 

Project lead/principal investigator (PI): Christian Hauck (Professor) 

Collaborators: Coline Mollaret (PhD student), Christin Hilbich (Senior Lecturer) 

External collaboration with:

  • PERMOS network
  • Dr. Joseph Doetsch (ETH Zurich)


Contact at University of Fribourg:
coline.mollaret[at]unifr.ch, christin.hilbich[at]unifr.ch, christian.hauck[at]unifr.ch


Research aims
:

1.  Improvement of geoelectrical and seismic data acquisition and data processing for continuous monitoring of permafrost thaw processes in alpine and polar areas

2.  Joint/coupled data processing and inversion schemes for thermal and geophysical data sets

3.  Quantitative approaches to estimate ground ice contents and their temporal changes

4. Relation of the obtained ice content changes to hydrological and kinematic processes in permafrost terrain.


Methods/methodology of the project
: Electrical Resistivity Tomography (ERT) and Refraction Seismic Tomography (RST), automatic weather station, soil moisture, borehole temperature. This project aims to establish a joint inversion of ERT and RST data for ice content quantification.

Study area: Swiss Alps: Schilthorn (BE), Stockhorn (VS), Murtèl-Corvatsch (GR), Lapires (VS).

Exemplary results:


Figure 1 Averaged specific resistivity for several depth layers in summer months (July until September) at Schilthorn since 1999. Colours represent depth layers. For the layers between 6 and 10 m depth, we can observe a first resistivity drop in 2003 (summer heatwave). Resistivity recovered to previous values in 2007. Since then, resistivity decreased continuously below 6 m depth. It leads to the conclusion that more water is present at depth (between 6 and 10 m) also meaning a lower ice content.

 

Figure 2 Borehole temperature and resistivity at 7 m depth at Schilthorn. The higher the temperature, the lower the resistivity. When temperature gets close to the melting point, soil resistivity drops (in 2003 and in 2010). Since 2010, the resistivity remained very low indicating that the water content (at 7m depth around the borehole) stayed high (and consequently, ice content did not recover since 2010).

 

References:

Hauck, C., Böttcher, M. and Maurer, H. (2011): A new model for estimating subsurface ice content based on combined electrical and seismic data sets. The Cryosphere, 5, 453–468.
Hilbich, C., Fuss, C., Hauck, C. (2011): Automated time-lapse ERT for improved process analysis and monitoring of frozen ground, Permafrost and Periglacial Processes 22(4), 306-319, DOI: 10.1002/ppp.732.

Unit of Geography - Chemin du Musée 4 - 1700 Fribourg - Tel +41 26 / 300 90 10 - Fax +41 26 / 300 9746
nicole.equey [at] unifr.ch - Swiss University