Spatial assessment of permafrost characteristics and dynamics in alpine periglacial environments
Zusammenfassung der Projektergebnisse
The research project "Spatial assessment of permafrost characteristics and dynamics in alpine periglacial environments" was concerned with the detailed analysis of shallow permafrost occurrences. Field sites were chosen to be within the limits of the Little Ice Age maximum glacier extent. Geophysical, thermal, and kinematic measurements were conducted in unconsolidated sediments of present-day glacier forefields. Detailed information on ground characteristics, active layer thickness and extent of the permafrost body was gained by 3D geophysical imaging. These spatial results are superior to existing 2D linear cross-sectional information of subsurface resistivity distribution. A more process-oriented finding was obtained from an automated geoelectric monitoring setup that enabled the analysis of time-dependent processes within the uppermost 2-4 meters of the subsurface by means of daily resistivity data. From this data set the annual accretion of ice at the permafrost table during the spring melt could be visualized (Murtèl/Corvatsch area). This transient layer at the active layer–permafrost boundary plays a crucial role for the stability of the permafrost system in unconsolidated sediments. Complementary data from up to 5 years of ground temperature monitoring show that the depth of the active layer at all three investigated permafrost sites in this project is rather constant in summer (Murtèl/Corvatsch area and Val Muragl). The transient layer acts as a buffer because it increases the latent heat required to thaw the permafrost beneath. However, temperature data inside the permafrost bodies show variability over time, this is also supported by multiannual geoelectric data sets. Hence, aggradation and degradation of ground ice may occur at close distance whereas at the same time the permafrost table remains at the same depth. As one of the most important factor for the micrometeorological regime at the ground surface the annual evolution and total thickness of the snow cover has been assessed. It highly influences the degree of undercooling that the ground surface experiences every winter. Beside the snow cover, the grain size of the surface substrate is another modulating factor. While it prevents the formation of a smooth snow cover it is crucial for the transport of heat into the ground. In consequence of numerous snow fall events during summer, detailed geomorphological and geophysical measurements could not be implemented at the research site Zugspitze. First data obtained in 2011 point to the existence of individual high-resistivity anomalies in the subsurface that may be related to ice-filled sink holes on the karstified Zugspitzplatt.
Projektbezogene Publikationen (Auswahl)
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(2012): Electrical resistivity monitoring for the detection of changes in mountain permafrost at different time scales. In: Supper, R. and Kauer, S. (Eds.): Berichte der Geologischen Bundesanstalt Österreich – International Workshop on geoelectrical monitoring. Book of extended abstracts. Wien
Kneisel, C., Rödder, T., Roth, N. and D. Schwindt
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(2012): Influence of snow cover and grain size on the ground thermal regime in the discontinuous permafrost zone, Swiss Alps. Geomorphology 175-176,176-189
Rödder, T. and C. Kneisel
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(2012b): Permafrost mapping using quasi-3D resistivity imaging, Murtèl, Swiss Alps. Near Surface Geophysics 10, 117-127
Rödder, T. and C. Kneisel
