Seasonal and diurnal freeze–thaw dynamics of a rock glacier and their impacts on mixing and solute transport

Abstract. Rock glaciers play a vital role in the hydrological functioning of many alpine catchments. Here, we investigate seasonal and daily freeze–thaw cycles of the previously undocumented Canfinal rock glacier (RG) located in the Val d'Ursé catchment (Bernina Range, Switzerland) and the RG's influence on the dynamics of the hydrogeological system. We combine digital image correlation techniques, geochemical and isotopic analyses, time series analysis, and hydrological monitoring to understand the functioning of the hydrological system. An acceleration of RG creep since 1990 has occurred, with the most active regions exhibiting horizontal velocities of ∼1 m yr−1. Distinct geochemical signatures of springs influenced by RG discharge reflect contrasting and temporally variable groundwater mixing ratios. A novel application of frequency–domain analysis to time series of air temperature and spring electrical conductivity enables a quantitative understanding of the RG thaw and subsurface flow dynamics. Following the onset of snowmelt, we observed a gradual decrease in the time lag between air temperature maxima and spring electrical conductivity minima at the front of the rock glacier. This suggests progressively increasing flows within the talus, driven by efficient recharge from snowmelt and contributions from the thawing rock glacier. Through our multi-method approach, we develop a conceptual model representing the main cryo-hydrogeological processes involved in RG-influenced alpine headwaters.