Mechanisms of Solute Transport in Ice-Supersaturated Debris: 2. Rock Glacier Hydrology in Alpine Glacial-Periglacial Systems

Abstract

Active rock glaciers represent permafrost-affected aquifers that store freshwater in alpine headwater catchments. Groundwater flow in these aquifers is altered by degrading permafrost and the development of preferential flow paths in the subsurface. Where these pathways connect to form channel networks, they significantly change solute and pollutant transport. This study analyzes the hydraulic properties of such channel networks at two active rock glaciers in the Austrian Alps through tracer tests and inverse transport modeling. At both rock glaciers, tracer clouds traveling down the channel network show fast advection and limited dispersion. Parts of the tracer are retarded in stagnant water zones along the flow paths, such as turbulent eddies and vortices, recirculation in cascades and pools, and dead-end passages between the blocks of the ice-debris mixture forming the frozen rock glacier cores. The patterns of water infiltration control the channel network structure: localized recharge strongly concentrates flow along a major channel, diffuse recharge results in a distributed network of smaller channels with diverging and converging flow paths. The hydraulic properties of these channel networks are crucial for assessing the vulnerability of permafrost-affected aquifers. They permit the rapid transfer and partial retardation of solutes, making them more susceptible to contamination—a growing concern as infrastructure development advances in high alpine environments.