Evidence of winter ascending air circulation throughout talus slopes and rock glaciers situated in the lower belt of alpine discontinuous permafrost (Swiss Alps)

The winter ascending circulation of air throughout an accumulation of coarse slope sediments (the so-called chimney effect) facilitates the cooling of the ground and even the occurrence of permafrost in the lower part of a deposit. Simultaneously, any freezing is unlikely to occur in the upper part. To date, the chimney effect has been reported mainly for cold and sometimes perennially frozen scree slopes situated at low elevations, far below the regional limit of the discontinuous mountain permafrost. This article reports observations made recently in the western Swiss Alps in several accumulations of coarse sediments (talus slopes, relict or inactive rock glaciers) located at higher elevations (2200–2800 m a.s.l.) within the belt of discontinuous permafrost or close to its lower limit. These observations show that a chimney effect may also occur in debris accumulations situated at ‘usual’ mountain permafrost elevation. This gives rise to multiple questions, in particular about the impact of the chimney effect on both the thermal regime and the spatial distribution of discontinuous mountain permafrost.

Keywords:

• air circulation
• discontinuous permafrost
• rock glacier
• Swiss Alps
• talus slope

Acknowledgements

Special thanks are due to Dr Martin Gude and the anonymous reviewers for their useful comments, and to Eddie Graham for editing the English text.