The degradation of ground ice in talus deposits, which are important forms of debris storage inmountain environments, can cause mass movements, subsidence or instability of mountain infrastruc-ture. Two 20 m deep boreholes instrumented with thermistors and located in a talus slope at 2400 m aslabove a lake at Flu ̈ela Pass in the eastern Swiss Alps allow the analysis of the evolution of groundtemperature and permafrost thickness between 2003 and 2008. The occurrence of intra-talus ventilationcan be discerned due to thermal anomalies within a layer of coarse blocks with large voids at around15 m depth near the base of the slope and at 10 m depth mid-slope. Intra-talus ventilation is particularlyeffective in winter when subzero air temperatures coincide with snow depths less than 50 cm andreverses to a gravity discharge of intra-talus air when air temperatures become positive. Despite thelack of annual variability in active layer depth, rapid permafrost degradation and thinning of groundice (from 7 m thickness to 3.5 m in 4 years) is currently occurring. It is attributed to latent heat transferfrom the moving air stream, caused by the flux of vapour from the relatively warm lake water table at20 m depth and its condensation at the base of the permafrost body.