Topographic and Geologic Controls on Frost Cracking in Alpine Rockwalls

Frost weathering is a major control on 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 predicted 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 but frost cracking patterns in terms of peak location and affected rock mass remained consistent between varying input parameters. Thermo-mechanical models incorporate rock strength and hydraulic properties and provided a frost cracking pattern at the rockwall scale that better reflects the measured fracture spacing. At the 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.

Automated summary

The study investigated rockwall erosion in Alpine environments by using temperature loggers and different frost cracking models in the Swiss Alps, finding that different parameters have a significant impact on crack size, but the peak location and affected rock mass remain consistent across varying parameters in crack patterns. Thermo-mechanical models incorporating rock strength and hydraulic properties showed better reflection of measured fracture spacing at the rockwall scale and increasing frost cracking with altitude at the mountain scale, contradicting purely thermal models but matching existing rockfall studies.