Active Layer Characteristics At Ten Borehole Sites In Alpine Permafrost Terrain, Switzerland

ABSTRACT This study investigates and compares active layer characteristics determined from ground temperature measurements at ten borehole sites in various types of Alpine permafrost terrain. Active layer thickness ( ALT ) remained fairly constant at the individual boreholes over the past five to 14 years, but was highly variable among the sites due to local terrain characteristics. To allow intra‐site comparisons, a characteristic depth within the active layer was determined for each site. The temperature series either measured or interpolated for that depth were used to investigate different thermal stages during the annual thawing and refreezing cycle. The relation between air temperature thawing‐degree days and ALT was investigated on an annual, seasonal and daily basis. The results show that at least daily data are required to establish the relevant characteristics of active layer development. Periods of slow advance of the thaw plane, interpreted as being due to the presence of ice‐bearing layers within the active layer, are particularly important to the final ALT . Rapid active layer deepening, however, can occur due to the formation of taliks caused by lateral thermal disturbances below the active layer. Copyright © 2012 John Wiley & Sons, Ltd.