1. INTRODUCTION
Rock glaciers, moraines and talus slopes as the most important alpine coarse-grained sediment deposits may play a critical role in providing groundwater discharge in alpine catchments (besides highly fractured or karstified bedrock aquifers) that sustain baseflow in larger river systems further downstream (Hayashi, 2020). Intact, particularly active rock glaciers on the one hand may store hydrologically valuable ice volumes (Jones et al., 2018) and on the other hand act as shallow groundwater storages or reservoirs in alpine headwaters (Jones et al., 2019; Wagner et al., 2020a; Winkler et al., 2016, 2018). To fully recognize the hydrological cycle in alpine regions, shallow groundwater systems such as rock glaciers need to be better understood in the light of climate change as these water storages / buffers are expected to be more resilient than e.g. ice glaciers (Jones et al., 2019; Wagner et al., 2019). In the last decades, investigations related to the hydro(geo)logy of rock glaciers were thus intensified (e.g. Harrington et al., 2018; Hayashi, 2020; Krainer & Mostler, 2002; Krainer et al., 2007; Winkler et al., 2016) and further research is warranted.
Rock glaciers evolve from active, downslope creeping rock-ice mixtures to inactive (still containing permafrost-ice, but not moving anymore) and further to relict, permafrost ice-free distinct debris accumulations (e.g. Barsch, 1996; Berthling, 2011)). Relict rock glaciers display a complex internal structure (e.g. Zurawek, 2003) and can be characterized as an aquifer with at least a fast and a delayed flow component (Pauritsch et al., 2015, 2017; Winkler et al., 2016). The delayed flow component is related to a fine-grained base layer representing the main shallow groundwater component, whereas lateral flow in the coarser upper layers allows generating a fast flow component.
Geophysical investigations and drillings showed that intact, permafrost-ice containing rock glaciers have an unfrozen base layer underneath the permafrost-ice-debris main body that is up to more than 10 m thick and contains high amounts of fine-grained sediment (Hausmann et al., 2007, 2012; Krainer et al., 2015). This unfrozen base layer is interpreted to be responsible for base flow during longer periods of little to no recharge (e.g. winter; Wagner et al., 2020a). Lateral flow on top of the permafrost body (within the active layer; e.g. Krainer et al., 2007; Winkler et al., 2018) or along channels within the permafrost body (related to talik formation; e.g. Arenson et al., 2010; Zenklusen Mutter & Phillips, 2012) might be responsible for a fast flow component. The actual contribution of potential permafrost ice melt is another component that needs further attention (besides increasing storage capacity due to melting of ice; cf. Rogger et al., 2017). In addition, cirque glaciers or remnants thereof in the upper catchment of a rock glacier provide recharge / melt water which may affect the flow dynamics of rock glacier springs and act as an additional runoff component (e.g. Wagner et al, 2020a) that might decrease when climate warming continues (Shannon et al., 2019).
The aim of this study is to (i) differentiate between various sources of recharge (namely rainfall, snowmelt and ice melt from cirque glaciers within the rock glacier catchment) and (ii) quantify the diurnal and seasonal patterns of the individual contributions in addition to groundwater to the discharge at the rock glacier springs. (iii) The ice melt contribution (from permafrost and cirque glacier) to spring discharge is discussed in the light of climate change and uncertainties of the methods applied. The quantification of individual flow and recharge components is achieved using a multidisciplinary approach and is considered as an important step towards a better understanding of climate change impact in alpine catchments.