ROCKING ALPS - Rockfall and Weathering in the Eastern Alps

The process of weathering and induced rockfall, particularly the generation of pore water pressure during freezing, is still not fully understood. A key to understanding is to gather data on rock moisture distribution and pore water displacement during freeze-thaw events. However, such data from natural rockwalls is extremely sparse if altogether present. The small scale 2D-resistivity profiling technique, as introduced by the applicant, allows spatially and temporally high resolution observation of moisture distribution in rock. Systematic monitoring during daily and annual freeze-thaw cycles is suitable for vitally advancing the state-of-the-art knowledge on frost weathering and subsequent rock detachment. For this purpose, a semi-automated monitoring program will be implemented in the north-eastern Alps (Gesäuse, Dachstein, Kitzsteinhorn), comprised of fixedly installed 2D-resistivity instruments with survey lines in northerly and southerly orientation. Additionally, rock temperatures, rock moisture, electrical conductivity and pore water pressure will be registered at different depths in high temporal resolution. While the measurements in the Gesäuse are carried out near to the valley floors (and thus, close to potentially endangered infrastructure), the test sites at Dachstein and Kitzsteinhorn are situated in high-alpine environment which allows to investigate the impact of permafrost und permafrost degradation on weathering. Moisture simulation calculations using the program WUFI will complement the investigations, allowing to cross-check the results from different techniques and to extrapolate the results to other topographical positions. Rockfall, being the output parameter of frost weathering, will be determined at test plots in the vicinity of the measuring instruments by means of wire mesh collectors and terrestrial laser scanning (TLS), allowing to rate the monitored frost events according to their effectiveness for weathering. The results will be compared to infrared photography to find relations between microclimatic parameters and weathering patterns. The results are thought to contribute to a better understanding of weathering processes at rockwalls, thus allowing to model and delimitate particularly weathering-prone areas and to predict times of heightened rockfall activity.

The process of frost weathering and subsequent rockfall, particularly the generation of pore water pressure during freezing, is still not fully understood. A key to understanding is to gather data on rock moisture distribution and pore water displacement during freeze-thaw events. However, such data from natural rockwalls is extremely rare if altogether present.To overcome this shortcoming, an automated monitoring program was installed at two study areas in the north-eastern Alps (in the Gesäuse national park at 800 m a.s.l. and on the Dachstein plateau at 2600 m a.s.l.). Both study areas are characterised by steep rock faces with the prevailing rock types Dachstein limestone (Dachstein) and Wetterstein dolomite (Gesäuse). Because of the very different altitudes, the impact of permafrost und permafrost degradation was also considered in the Dachstein area. In both areas, different types of sensors were installed at north and south exposed rock walls to get insight on moisture and temperature fluctuations during freeze-thaw cycles. Electrical resistivity and heat capacity sensors were used, both reacting on pore water saturation and its fluctuations. Freezing of pore water leads to a very sharp increase in resistivity and to a drop in heat capacity, respectively, which enables the direct observation of freezing processes. Increasing water content was observed in the vicinity of ice formations; these are caused by water being thrusted away from the freezing front with the potential of generating hydrostatic pressures, and by slow water movement towards the freezing front (ice segregation. Both processes can potentially cause frost weathering and subsequent rockfall. The continuous monitoring of rock moisture at a natural rock face was realised for the first time and delivered unique data which aids to understand frost weathering. It is planned to use the results for rockfall susceptibility mapping and for the development of early warning systems.