The influence of a rock glacier on the riverbed hydrological system

Abstract. Climate change is accelerating cryosphere degradation in mountain regions, and altering hydrological and geomorphological dynamics within deglaciating catchments. Rock glaciers, which degrade slower than glaciers, can exert a prolonged influence on water resources in alpine watersheds. This study investigates both the direct and indirect influences of a rock glacier on the Shár Shaw Tagà (Grizzly Creek) riverbed in the St. Elias Mountains (Yukon, Canada). We applied a unique multimethod approach combining hydro-physicochemical and isotopic characterization, drone-based thermal infrared (TIR) imagery, and visible time-lapse imagery. Results reveal that the rock glacier's geomorphic and thermal properties constrain the riverbed and its underlying alluvial aquifer, driving shallow groundwater resurgence. These indirect disruptions promote downstream cryo-hydrological processes by facilitating aufeis formation and modifying the physicochemical properties of surface water. In contrast, direct hydrological influence from the rock glacier's internal drainage system to downstream surface waters appears minimal. This configuration is transitional, as the constraint imposed by ground ice is expected to diminish with progressive permafrost degradation. Overall, this study identifies the critical yet transient role of rock glaciers in alpine hydrology. Beyond their internal hydrological behaviour, they shape catchment hydrology through geomorphic controls. Our findings highlight the need to account for indirect effects when evaluating hydrological dynamics in deglaciating catchments.