Sediment transport in the rapidly changing paraglacial zone of a high alpine catchment

Abstract:

Glacier retreat is the most visible manifestation of climate change in alpine areas over the past 150 years and has a significant impact on high mountain runoff and, thus, on sediment transport in headwaters. Concurrent degradation of permafrost in headwalls exposed by downwasting ice and in periglacial hillslopes alongside glaciers causes increasing sediment flux onto glacier surfaces. The accumulation of supraglacial debris at the current glacier tongues promotes an important source of sediment in the proglacial zones. Changing water supply from retreating glaciers alter stream discharges from mainly continuous transport of unconsolidated sediments (supply-limitation) towards pronounced variations between sedimentation at low water runoff and erosion at high runoff events (transport-limitation) in a generally unstable paraglacial landscape.

The Hidden.ice project intends to investigate the connection of coarse sediment including supraglacial debris from the proglacial transition zone to downstream fluvial transport. A detailed study of debris deposition and renewed movement by fluvial transport is performed at the LTER site Jamtalferner (Austria), combining hydrological modelling of the potential transport capacity of sediments in the glacial stream with the calculation of sediment volume changes from UAV-based photogrammetry. A complementary documentation of the historical evolution of the channel network from satellite images and historical maps will increase our knowledge of the temporal evolution of the sediment-rich proglacial zone which has evolved with glacier retreat since the 1850s.

First results show an accumulation of sediments in the proglacial area where the glacier has retreated over the past years. An increasing share originates from the extensive supraglacial debris cover evident on the current glacier surface. Strong spatial variations in the course of the stream suggest a high connectivity of the entire proglacial sediment body to bed load transport, and considerable shifts of the main channel are documented. Historical information and remote sensing data show sediment cascades that formed further downstream with the retreat of the glaciers in the last decades and also indicate substantial changes.