PACE: Permafrost and climate in Europe - climate change, mountain permafrost degradation and geotechnical hazard

• Unité de recherche: PCRD EU
• Numéro de projet: 97.0054-1
• Titre du projet anglais: PACE: Permafrost and climate in Europe - climate change, mountain permafrost degradation and geotechnical hazard

Mots-clé (Anglais)

Environmental protection; mountains; permafrost; geothermal monitoring; modelling; climate change; geotechnical hazards

Programme de recherche (Anglais)

EU-programme: 4. Frame Research Programme - 3.1 Environment

Description succincte (Anglais)

See abstract

Partenaires et organisations internationales (Anglais)

Coordinator: University of Wales (UK)

Résumé des résultats (Abstract) (Anglais)

In the final year of the project the work was focussed on data processing and the development of new geophysical data inversion schemes. Additional geophysical field work was conducted on the permafrost monitoring site at Schilthorn, Swiss Alps, where a geoelectric monitoring system was installed at the end of 1999, and at Tarfala, Sweden. Furthermore, electromagnetic soundings (with the PROTEM system) were conducted on several permafrost test sites in Switzerland to improve the data base for PROTEM applications on mountain permafrost. A miniature DC resistivity system was developed to examinate the influence of freezing and thawing processes on the resistivity for different materials and water contents. The lab results were used to estimate the unfrozen water content on the permafrost monitoring site on Schilthorn. For the first time, passive microwave radiometry was applied from a board a helicopter to deterime remotly permafrost distribution arrays. The results were in good agreement with standard surface-based measurements.
The Swiss 100m deep drillings at Schilthorn and Stockhorn (by the German partner) were completed in summer 2000. At Schilthorn an additional oblique 100m borehole was drilled to study the influence of the peak-topography on the thermal regime.
Geophysical data processing included the application of 2-dimensional tomographic inversion schemes for DC resistivity and refraction seismic data. The results showed a large applicability of this approach even for sparse data sets and extreme value contrasts. The inversion successfully delineated the extremely high-resistive main part of rock glaciers, as well as isolated ice occurrences with spatial dimensions of a few metre. The combined application of DC resistivity and refraction seismic allowed the differentiation between ice-,air- and rock anomalies, each showing similarly high resistivity values, but different seismic velocities. Additional modelling studies using synthetic data sets confirmed the large potential of these inversion schemes for different permafrost targets.
The geoelectric monitoring system at Schilthorn was used to monitor the seasonal variations of resistivity over a full year. Measurements were conducted approximately each month using a fixed-electrode system, which was accessible throughout the year. Through tomographic inversion, spatially variable and transient processes like the advance and retreat of freezing fronts could be monitored. The results were combined with temperature data from the borehole as well as data from laboratory experiments to estimate the evolution of the unfrozen water content in the uppermost 10 metre. This approach is very suitable for future permafrost monitoring programmes especially in spatially heterogeneous regions.
The results of all geophysical surveys during the PACE project were analysed to determine the suitability of each method for various permafrost problems. The findings were published as part of the PhD-thesis of Christian Hauck (ETH Zürich), which was finished in April 2001.

Références bases de données (Anglais)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0054-1