Rilevamento del permafrost con il metodo BTS (Bottom temperature of the Winter Snow Cover) nell’Alta Valtellina (Sondrio, Italia)

Permafrost mapping with BTS methodology in the Upper Valtellina (Sondrio Province, Italy)

Abstract

At the end of the 1992 and 1993 winters, 285 BTS (Bottom Temperature of the Winter Snow Cover) measurements were carried out in four areas of the Upper Valtellina (Northern Italy). The BTS is a quick and inexpensive method to map the occurrence of permafrost and/or buried ice. This method is based on the fact that the surficial temperature of the ground beneath the snow cover at the end of the winter reflects the amount of heat stored by the ground during the summer season and the Earth heat flow. According to literature values of BTS below -3° C point out the high probability of the occurrence of permafrost, whereas temperatures ranging between -1.7 and -3°C suggest its possible presence. In the investigated areas the BTS temperatures range between O.O° C and -10.1° C. In particular, very low BTS temperatures (min. -10.1°C; max. -3.0° C) were recorded on rock glacier named Pizzo Filone III. The measurements carried out in the studied areas indicated that the presence of permafrost is concentrated in active rock glaciers, Polygenetic active alpine cones and subordinately in glacial deposits and inactive rock glaciers. The permafrost distribution is also irregular within active rock glaciers but it seems concentrated in their frontal and apical parts.