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

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. 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. A gradual decrease in time-lag between air temperature maximum and spring EC minimum, caused by dilution from RG ice melt, is observed over the snow-free period, implying progressively shorter residence times. Through our multi-method approach, we develop conceptual models for RG-influenced alpine hydrogeological systems on daily and seasonal time-scales.