A rapidly moving small rock glacier at the lower limit of the mountain permafrost belt in the Swiss Alps

Surface and internal movements, structure and thermal conditions were investigated on a small talus-derived rock glacier in the Upper Engadin. A borehole 5.4 m deep drilled on the upper part of the rock glacier displayed ice-saturated sediments, consisting of pebbles, cobbles and fine debris. The mean annual temperatures were close to 0°C within the uppermost 5 m of ground. Whereas the lower part moved downslope only slightly, the upper part showed rapid movement (50–150 cm a 1), accelerating over a 3-year period. Inclinometers also showed large deformation of permafrost at depth. A DC resistivity tomogram indicates that permafrost is thinner than 20 m. Permafrost close to the melting point is deformed rapidly and is sensitive to inter-annual variation in ground temperature. Such rapid movement is considered to be temporary and eventually followed by inactivation of the rock glacier because of permafrost melting and a lack of debris input. Permafrost, Phillips, Springman & Arenson (eds) © 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7

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