This study discusses rock glaciers as climate sensitive elements of the cryosphere. The study consists of three research papers. Some additional publications are provided in the appendix.
The first paper discusses the long-term time series of terrestrial surface displacement measurements at Outer Hochebenkar rock glacier, the main study site for this thesis. Velocities have been increasing significantly in recent years. Velocity variations correlate poorly with temperature and precipitation parameters when considering absolute values, but improve for the respective cumulative sums. Mean annual air temperature and summer precipitation are found to be important factors that can explain some of the long term velocity variations. Comparing the results from Outer Hochebenkar with data from other sites shows that decadal-scale trends in surface movement are similar at various rock glaciers throughout the Alps, whereas smaller inter-annual variations differ between the sites.
Paper 2 presents GPR (ground penetrating radar) data from Outer Hochebenkar rock glacier. A simple numerical model based on Glens flow law is developed to approximate the thickness of the rock glacier based on measured flow velocities. The results are compared with the GPR data. A number of assumptions about the internal structure of the rock glacier have to be made for the processing of the GPR data and these assumptions are partially adjusted based on the model results. The paper includes a detailed discussion of the uncertainties and limitations associated with the GPR data acquisition and processing and the modelling approach. It is argued that ice rheology can be applied to rock glaciers if certain conditions are fulfilled. Glens flow law is useful as a first order approximation of rock glacier movement and some insights about rock glacier composition can be gained even from simple modelling approaches. However, there is a need for more refined models and more ground truth data to improve our understanding of rock glacier rheology.
Paper 3 discusses recent results of mass balance monitoring at two small Alpine glaciers. The glaciers are similar in size but precipitation patterns differ at their respective locations in the Hohe Tauern and Dachstein ranges and mass balance parameters differ accordingly. Glacier mass balance can show significant spatial variability corresponding to local weather conditions, as exemplified by the two glaciers discussed in the paper. However, pronounced long-term trends of glacial recession or advance are governed by global climatic trends. The acceleration detected at a number of rock glaciers in recent years is presumably also due to a common climate forcing, yet this phenomenon is far less universal than current trends of negative glacier mass balance. Rock glaciers show a greater range of systemic response to climate forcing. Whereas the relationship between glaciers and climate can be considered linear in a very general sense, rock glaciers exhibit the non-linear threshold responses and positive feedback mechanisms of a nonequilibrium system.