Water origin and quality of rock glacier springs. Case studies in the Swiss Alps.

While the knowledge of the dynamics and internal structure of rock glaciers is well developed, a lack of understanding of their hydrological functioning is observed in the scientific literature. In particular, the origin and the quality of the water emerging from rock glaciers are not well known, together with its contribution to aquatic systems. Since rock glaciers are becoming increasingly important water sources under the influence of climate change, it is essential to improve knowledge about the modification of the hydrological regime of these high altitude debris accumulation, in particular by tracing ice melt in rock glacier outflows, and to quantify the impact of ground ice melting on the hydrochemistry of Alpine water systems. In this research, we combined isotopic and physico-chemical analyses for six rock glacier outflows in the Swiss Alps during the 2020 summer season. Chemical and isotopic analyses were also performed in sources not fed by rock glaciers at all study sites. The ionic content (SO₄^2-, Ca²⁺, Mg²⁺, NO₃^-) measured in water emerging from active rock glaciers and ice-patches was higher than that detected in sources not fed by rock glaciers. Water emerging from active rock glaciers and ice-patches was also characterized by an increase in electrical conductivity and in ionic content (SO₄^2-, Ca²⁺, Mg²⁺), and by isotopic (δ¹⁸O) enrichment during the warm season. The seasonal evolution of these physico-chemical and isotopic parameters could indicate the water supply related to ground ice melting in water emerging from active rock glaciers and ice-patches. We assume that the cryosphere stored atmospheric pollutants and other chemical elements during a colder period in the recent past (1960s-1980s) and that the current melting of rock glacier ice releases these chemical compounds in the Alpine water systems. The hydro-chemical processes taking place in active rock glaciers were summarized in a conceptual model based on the results of this study.