Original paper

Monitoring nourishment processes in the rooting zone of an active rock glacier in an alpine environment

Kellerer-Pirklbauer, Andreas; Rieckh, Matthias

Abstract

This paper presents up to eight years (2006 – 2014) of data that address geomorphic and nival processes at the rooting zone of the active Hinteres Langtalkar Rock Glacier, Hohe Tauern Range, Austria. We used a remote digital camera system which took daily images from the main rooting zone of the rock glacier and the rockwall above. 1,383 images were available for the analysis. Rock temperature monitored at three shallow borehole sites and an automatic weather station allowed the assessment of potential weathering rates. Climate data from a nearby meteorological observatory were additionally used to consider long-term changes. Results indicate that neither snow and ice nor sediments have been transported in large quantities to the rock glacier system during the observation period. Notable mass movement was only detected during six events (3 rockfalls, 3 debris flows). Perennial snow patches in the rooting zone of the rock glacier were observed in 4 out of 9 years. Diurnal freeze-thaw cycles (FTC) occurred twice as often at the south-facing rockwall site compared with the north-facing site. Effective FTC (i.e. heating > 2 °C and subsequent cooling < – 2 °C) are only relevant at the south-facing site. The duration of the frost-cracking-window (temperature – 3 to – 6 °C) is about 10 times longer at the north-exposed rockwall. Permafrost is sparse at the south-facing slopes whereas widespread at the north-facing slopes overlooking the rock glacier. These observations suggest that segregation ice formation is more relevant for rock weathering at the north-facing rockwall producing larger clasts. In contrast, volumetric expansion during freezing might be the major control for rock weathering at the south-facing rockwall forming smaller debris. However, highly variable snow cover conditions in the rockwalls above the rock glacier influence substantially the thermal regime and hence potential bedrock weathering. We conclude that the present rate of rock glacier nourishment is not in equilibrium with the mass transport (sediment and ice) of the rapidly moving and disintegrating rock glacier. The studied rock glacier is in a state of detachment from its sediment and ice source. Topographical data further support a generally negative mass balance of the rock glacier during at least the last six decades.

Keywords

rock temperature monitoringfreeze-thaw cyclesautomatic digital camera (rdc)rock glacier nourishmentfrost weatheringhohe tauern rangehinteres langtalkar rock glacier