Abstract

Frost weathering is a major control of rockwall erosion in alpine environments. Previous frost cracking model approaches used air temperatures as a proxy for rock temperatures to drive frost weathering simulations on rockwall and on mountain scale. Unfortunately, the thermal rockwall regime differs from air temperature due to topographic effects on insolation and insulation, which affects frost weathering model results and the resulting erosion patterns. To provide a more realistic model of the rockwall regime, we installed six temperature loggers along an altitudinal gradient in the Swiss Alps including two logger pairs at rockwalls with opposing aspects. We used the recorded rock surface temperatures to model rock temperatures in the upper 10 m of the rockwalls and as input data to run four different frost cracking models. We mapped fracture spacing and rock strength to validate the model results. Our results showed that frost cracking models are sensitive to thermal, hydraulic and mechanical parameters that affect frost cracking magnitude, while frost cracking patterns in terms of peak location and affected rock mass were consistent. Thermo-mechanical models incorporate rock strength and hydraulic properties and provided a frost cracking depth pattern at rockwall scale that reflects better measured rock strength and fracture spacing of the simulated rock masses. On mountain scale, these models showed a pattern of increasing frost cracking with altitude, which is contrary to purely thermal models but consistent with observations of existing rockfall studies.