Applied geophysical methods in mountain and polar regions

Geophysical methods are very useful techniques for characterising and monitoring of the subsurface and can be applied to a large variety of problems within the cryospheric sciences, geomorphology, hydrology, geophysics, geology, forestry and agriculture, engineering, material science and many others.

Within our group we mainly apply electrical, electromagnetic and seismic methods for analysing processes in the near subsurface (- 100m depth).

In addition, we develop new data processing techniques, such as improvements for the filtering and inversion of geophysical data sets, reliability analyses and monitoring strategies. We conduct geophysical studies in all kind of terrain with a specialty of applications in high mountain areas. 

 

Ground ice distribution and volumetric content in rock glaciers in the Chilean Andes – a comparison of geophysical data and ground truth from boreholes

Rock glaciers are a widespread phenomenon in the periglacial belt of the South American Andes. Within the context of the projected water shortage in the arid mountain regions as a consequence of continued climate change, the significance of these rock glaciers for the hydrological cycle is currently being discussed in a controversial way. Given the lack of comprehensive field measurements and quantitative data on the local variability of rock glacier internal structure, ice content and their hydrological contribution, an extensive site investigation campaign and periglacial monitoring program was initiated in the basin of Rio Choapa, located in Chilean Andes of the Coquimbo Region. The overall objective of this initiative is to assess runoff from the permafrost, in particular from the rock glaciers in the basin. Therefore it is critical to evaluate the ground ice content and its spatial distribution, which includes important parameters such as overall permafrost thicknesses, active layer thicknesses and volumetric ice contents. Rock glaciers and protalus ramparts are of special focus as they are considered being the main pool of ground ice in the basin.

Geoelectric and refraction seismic tomography is used to map and describe the structure of the ground ice of the rock glaciers and other areas of the basin. Further, both geophysical methods are combined in a quantitative approach to model the volumetric ice content and its spatial variability using the so-called 4-phase model (Hauck et al. 2011, Pellet et al. 2016). The resulting data are compared with qualitative and quantitative ground truth data on structure and volumetric ice content from eight boreholes with undisturbed frozen core extraction drilled at the same sites. These results will be used in a following step to better assess future runoff evolution from degrading permafrost in rock glaciers under ongoing climate change.

Duration: 2016-2018

Project lead/principal investigator (PI): L. Arenson (BGC Engineering, Vancouver, Canada) 

Partner(s): Department of Geosciences, University of Fribourg

Collaborators: Christian Hauck, Christin Hilbich, Coline Mollaret 

External collaboration with:

  • BGC Engineering, Vancouver & Santiago

Contact at University of Fribourg: christin.hilbich@unifr.ch, christian.hauck@unifr.ch

Publications:

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, Mollaret C, Perrenoud J, Wicki A, Wicky J, Hauck C, Arenson L, Wainstein P (2016): Ground ice distribution and volumetric content in rock glaciers in the Chilean Andes – a comparison of geophysical data and ground truth from boreholes. Poster presentation XI. International Conference on Permafrost, 20 - 24 June 2016, Potsdam, Germany.

Pellet C, Hilbich C, Marmy A and Hauck C (2016) Soil Moisture Data for the Validation of Permafrost Models Using Direct and Indirect Measurement Approaches at Three Alpine Sites. Front. Earth Sci. 3:91. doi: 10.3389/feart.2015.00091.

 

Research aims/sciences questions:
(1) Determination of permafrost distribution and ice content in various rock glaciers and talus slopes in the investigation area

(2) Evaluation of the accuracy of the 4PM
(3) Calibration of the 4PM with ground truth from drill cores

(4) Assessment of future runoff evolution from degrading permafrost in rock glaciers under ongoing climate change

Methods/methodology of the project: Electrical Resistivity Tomography (ERT), Refraction Seismic Tomography (RST), 4-phase model (4PM)

Study area: Basin of Rio Choapa, Coquimbo Region, Chilean Andes

Exemplary results:

Figure 1. Mapping of ice-rich permafrost in a rock glacier in the Rio Choapa basin using ERT and comparison with ground truth from drilling.


Improvement of geophysical monitoring routines for permafrost research

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.

SOMOMOUNT (Soil moisture monitoring in mountain areas)

TEMPS (The evolution of mountain permafrost in Switzerland)

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