Abstract
Abstract. Talus slopes are a widespread geomorphic feature in the Alps. Due to their high porosity a gravity-driven internal air circulation can be established which is forced by the gradient between external (air) and internal (talus) temperature. The thermal regime is different from the surrounding environment, leading to the occurrence of permafrost below the typical permafrost zone. This phenomenon has mainly been analysed by field studies and only few explicit numerical modelling studies exist. Numerical simulations of permafrost sometimes use parameterisations for the effects of convection but mostly neglect the influence of convective heat transfer in air on the thermal regime. In contrast, in civil engineering many studies have been carried out to investigate the thermal behaviour of blocky layers and to improve their passive cooling effect. The present study further develops and applies these concepts to model heat transfer in air flows in a natural-scale talus slope. Modelling results show that convective heat transfer has the potential to develop a significant temperature difference between the lower and the upper parts of the talus slope. A seasonally alternating chimney-effect type of circulation develops. Modelling results also show that this convective heat transfer leads to the formation of a cold reservoir in the lower part of the talus slope, which can be crucial for maintaining the frozen ground conditions despite increasing air temperatures caused by climate change.
Highlights
Mountain permafrost is currently undergoing substantial changes due to climate change as a whole and especially due to the observed air temperature increase
The ascending air flow within the talus slope can be clearly seen, with maximum flow velocities of around 100 m day−1, i.e. ∼ 0.001 m s−1, which is in the range of the values estimated in other model and observational studies (Tanaka et al, 2000)
The air circulation causes aspiration of cold atmospheric air into the lower part of the talus slope, where the lowest temperatures are found. This temperature distribution is a clear effect of the induced convective air circulation
Summary
Mountain permafrost is currently undergoing substantial changes due to climate change as a whole and especially due to the observed air temperature increase. Natural air convection with upward transport of warmer air from the permafrost body and downward transport of cold air from the surface can take place within the coarse blocky layer, both vertically (in flat terrain) as well as in form of a 2-D circulation within a slope. These two effects lead firstly to much lower surface and subsurface temperatures for terrain with coarse blocky surface layers compared to fine-grained or bedrock surfaces This permafrost mostly occurs in undercooled scree and talus slopes and has been well researched in a number of publications (Funk and Hoelzle, 1992; Wakonigg, 1996; Kneisel et al, 2000; Gude et al, 2003; Sawada et al, 2003; Delaloye et al, 2003; Gorbunov et al, 2004; Delaloye and Lambiel, 2005; Zacharda et al, 2007; Morard et al, 2008a, b; Phillips et al, 2009; Gadek and Leszkiewicz, 2012; Stiegler et al, 2014; Kneisel et al, 2015)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
