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.