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| Titel |
Geophysical Characterization of unstable Permafrost in the Turtmann Valley, Switzerland. |
| VerfasserIn |
K. J. Merz, H. R. Maurer, L. Rabenstein, T. Buchli, S. M. Springman |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060118
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| Zusammenfassung |
| Rising air temperatures in high mountain areas, caused by global warming, can lead to
permafrost degradation, which may induce ground instabilities and landslides. To
understand the associated thermo-hydro-mechanical (THM) processes associated
fully, a detailed geotechnical, geophysical and hydrological characterization of
a permafrost soil is needed. Based on this characterization, THM models can be
developed to predict general permafrost behavior under changing environmental
conditions.
A rock glacier in the Turtmann Valley, Switzerland has been selected for this
study. It shows signs of degradation as well as displacements of up to several meters
per year in some areas. The processes that cause these phenomena are still poorly
understood.
Extensive geophysical and geotechnical measuring and monitoring campaigns have been
carried out over the last two years to delineate (i) the volume of the rock glacier, (ii) the
occurrence of ice and (iii) the distribution of internal shear horizons. Seven boreholes, each
approximately 25m deep, were drilled to obtain geological information. The boreholes were
equipped with thermistor chains and inclinometers to monitor temperature and displacements
over time. First results indicate that the displacement is focused in a narrow zone at a depth of
about 15 m. Geophysical measurements include so far four seismic lines, two geoelectrical
profiles, one 3D geoelectric survey, several georadar profiles and cross-hole radar
measurements. The seismic data were analyzed with refraction tomography, and
the resulting tomograms allowed gross internal structures to be identified. They
indicate that a bedrock barrier subdivides the rock glacier in two flow branches
in its lower part. This agrees well with visual observations made at the surface.
Tomographic inversion of the geoelectric data show that the central part of the rock
glacier is ice-rich, whereas its front and sides are mostly ice-free. Furthermore
there are indications of ice loss in the degradation zone. The georadar profiles,
collected over the central part of the rock glacier, allowed the identification of several
internal shear horizons. One of them lies at a depth of about 15 m, and is therefore
interpreted as the currently active shear plane. By combining all the geotechnical,
geophysical and surface measurements, we are currently establishing a comprehensive
subsurface model, which will form the basis for subsequent numerical THM modeling. |
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