Role of Sparsely Glacierized Basins and Groundwater in Semiarid Andes Periglacial Headwaters

Abstract

A better understanding of headwater hydrogeology in the semiarid Andes is critical because high-elevation basins are considered water towers for the main valleys, where water demand is over-allocated. While the body of literature generally focuses on the contribution of glaciers to streamflow, there is little information on the contribution of sparsely glacierized basins and the origins and processes of groundwater generation at high elevations. The Corrales catchment in North-Central Chile contains both heavily and sparsely glacierized sub-basins as well as the highest public borehole in the region, making it suitable to fill such scientific gaps. Geophysical surveys and a pumping test were carried out to obtain information on groundwater flows beneath the Tapado terminal rock glacier and a main tributary of the Elqui River. Radioactive and stable isotopes were used to characterise the hydrological connectivity and the origins of water in the headwater basins. Low electromagnetic velocities and resistivities indicate the presence of liquid water beneath the rock glacier, suggesting the upper limit of a proglacial aquifer. The downstream valley aquifer appears transmissive and dominated by old waters (several decades) that are a mix of high-glacierized and sparsely glacierized basins. In addition, stable isotopes reveal distinct signatures for high-glacierized and sparsely glacierized basins, which may be attributed to isotope fractionation. These results suggest that water isotopes can be used to distinguish between waters originating from high-glacierized and sparsely glacierized basins. The study also identifies the presence of old waters in the sparsely glacierized basins, which indicates long-term storage, slow release or slow turnover times. This finding is crucial for understanding the evolution of late-season baseflow and streamflow in the context of climate change. As the contribution of such basins to total streamflow is significant, a better understanding of hydrological processes in sparsely glacierized regions is required.