Influence of glacial sediments on the chemical quality of surface water in the Ulta valley, Cordillera Blanca, Peru

•Mineralogical composition of proglacial tills is related to source area lithology.•Proglacial tills may act as reservoirs for precipitation.•Effects of proglacial tills on water quality are related to till composition.•These effects on water quality do not propagate strongly downstream.