PERMAFROST AND PERIGLACIAL PROCESSES Permafrost and Periglac. Process. 15: 299–307 (2004) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ppp.501 Rock-wall Temperatures in the Alps: Modelling their Topographic Distribution and Regional Differences Stephan Gruber,* Martin Hoelzle and Wilfried Haeberli Department of Geography, Glaciology and Geomorphodynamics Group, University of Zurich, Switzerland ABSTRACT Rising temperatures or the complete thaw of permafrost in rock walls can affect their stability. Present as well as projected future atmospheric warming results in permafrost degradation and, as a consequence, makes knowledge of the spatial distribution and the temporal evolution of rock temperatures important. Rock-face near-surface temperatures have been measured over one year at 14 locations between 2500 and 4500 m a.s.l. in the Alps. Different slope aspects have been included in order to capture the maximum spatial differentiation of rock temperatures. These data were used to further develop and verify an energy-balance model that simulates daily surface temperatures over complex topography. Based on a 21-year (1982–2002) run of this model, spatial patterns of rock-face temperatures in the Swiss Alps are presented and discussed. This model provides a basis for the re- analysis of past rock-fall events with respect to permafrost degradation as well as for the simulation of future trends of rock temperatures. Furthermore, the spatial patterns of rock-wall temperatures provide a quantitative insight into the topography-related mechanisms affecting permafrost distribution in Alpine areas without local influence from snow cover or an active layer with a complex thermal offset. Copyright # 2004 John Wiley & Sons, Ltd. KEY WORDS: rock temperatures; rock faces; Alps; mountain permafrost; energy balance; slope instability; rock fall INTRODUCTION Warming and thawing of permafrost can affect the stability of perennially frozen rock walls (Gruber et al., 2004; Haeberli and Beniston, 1998). The thaw of ice-filled rock joints can open them to groundwater migration, raising water pressures (Haeberli et al., 1997), and thus reduce the effective normal stresses. Davies et al. (2001) have shown that even the warm- ing of ice in rock joints can result in reduced stability. Slopes that are stable when several degrees below freezing or when ice free could be destabilized in the temperature range between 1.5 and 0  C. The transfer of these findings to the natural envir- onment (cf. No ¨tzli et al., 2003) requires knowledge about the spatial distribution of rock-wall tempera- tures and their evolution over time. Understanding and modelling of the processes that determine rock-face temperatures will also provide a means of assessing ranges of probable sub-surface temperatures caused by climate forcing and would provide a basis for assessing the impact of climatic change on rock-wall stability. In comparison with debris-covered slopes, rock faces react quickly to climate change. This is due to the absence of a block layer (Harris, 1996; Harris and Pedersen, 1998; Mittaz et al., 2000; Hoelzle et al., 2001) and corresponding direct coupling of surface Received 6 January 2004 Revised 29 June 2004 Copyright # 2004 John Wiley & Sons, Ltd. Accepted 29 June 2004 * Correspondence to: Stephan Gruber, Department of Geography, Glaciology and Geomorphodynamics Group, University of Zurich, Winterthurerstrasse 190, CH 8057, Switzerland. E-mail: stgruber@geo.unizh.ch