The role of proglacial rock glaciers in redistributing glacial meltwater

Abstract

The deglaciation of high mountain ranges is leading to the expansion of proglacial areas, which encompasses diverse permafrost and ground ice landforms. These features exert an increased influence on the hydrology and hydrogeology of alpine catchments as glaciers retreat. Despite the heightened attention received by rock glaciers for the last decades, their role within the broader hydrological and hydrogeological valley system remains understudied. Previous studies have highlighted rock glaciers’ ability to act as hydrological storage and to buffer water release from alpine catchments. However, there is a lack of studies about their ability to modify the groundwater flow paths in a proglacial valley system and to redistribute glacial meltwater. This study addresses this knowledge gap by investigating how the rock glacier redistributes glacial meltwater in a study catchment. Shar Shäw Tágà (Grizzly Creek) is a subarctic glaciated catchment located in the St. Elias Mountains, Yukon (Canada) that experiences significant glacial retreat. A non-relict rock glacier at the outlet of a glacial sub-catchment obstructs the valley thalweg, with only a few springs exhibiting minimal discharge from its front. These minor springs contrast remarkably with the substantial discharge observed at higher elevations above the rock glacier. Water level, water temperature and electrical conductivity variables were monitored in identified springs throughout the summer 2022. Results were compared to meteorological data with wavelet coherence analysis to determine the springs’ origins and drivers. Additionally, multiple sampling campaigns were conducted in the summers of 2022 and 2023 to analyze major ions concentrations and water stable isotopes signatures in the catchment’s streams. The results reveal that the rock glacier serves as a critical obstacle and deflector to subsurface meltwater, either forcing upstream meltwater to penetrate deeper into the subsurface, or redirecting lateral subsurface flow to resurge at its front, forcing part of the alluvial floodplain shallow aquifer to reach the surface. While rock glaciers are often considered potential water reservoirs, this study illuminates their dual role as critical deflectors for shallow subsurface flow in proglacial valley systems. They can impede glacial meltwater flow, originating alternative pathways toward deep aquifers or lowlands’ surface waters. Such findings nuance the ability of rock glaciers to store and release glacial meltwater, as they can deflect shallow subsurface flow. Additionally, it shows that rock glaciers can force infiltration and resurgence of water at specific locations, affecting the broader mountain hydrogeological system. Furthermore, it enforces their critical role in the future of water resources supplied by high mountain ranges in a deglaciation context.