No abstract

Displacement rates of mountain slope deformations that can affect entire valley mountain flanks are often measured spatially distributed in‐situ without spatial significance. The spatially explicit measurement and recording of time series of slope deformations is a challenge, as the unstable slopes are often disintegrated into several subdomains, which move with different deformation rates. The current state‐of‐the‐art monitoring systems detect slow to very slow deformation rates between mm/a and several m/a. Using the examples of slope deformations in Saalbach‐Hinterglemm and the deep rock slide Marzellkamm in Austria this paper presents the results of terrestrial laser scans, extensometer measurements, Spaceborne InSAR data, unmanned Aerial System Photogrammetry (UAS‐P), and fixed‐point measurements. The different measurements complement each other and are optimally aligned for different application areas. InSAR data can help to identify hot spots on regional and local scale, while UAS‐P enables for spatially high level accuracy in the detection of subdomains moving at different speeds. For local warning systems TLS, extensometers and GBInSAR deliver higher accuracy.

A rock slide on top of the clayey-silty-sandy-pebbly masses in the Gschliefgraben (Upper Austria province, Lake Traunsee) having occurred in 2006, together with the humid autumn of 2007, triggered a mudslide comprising a volume up to 4 million m 3 and moving with a maximum displacement velocity of 5 m/day during the winter of 2007-2008. The possible damage was estimated up to 60 million € due to the possible destruction of houses and of a road to a settlement with intense tourism. The movement front ran ahead in the creek bed. Therefore, it was assumed that water played an important role. Inclinometer measurements showed that a less permeable layer was sliding on a thin, more permeable layer. During the last centuries, mudslides had already pushed farms into the lake, as reported by chronicles. Thus, the inhabitants of 46 houses had to be evacuated for safety reasons. They could return to their homes after displacement velocities had decreased. It was decided (a) to prevent soaking of water into the uppermost, less permeable layer by transversal drainages, (b) to lower the pore water pressures by longitudinal trenches filled with blocky material, (c) to pump water out of the more permeable layer by well drillings upslope of the houses in order to create a stable block below the houses and (d) to remove material thrust over the stable blocks in order to avoid damage to the houses. These mitigation measures costing 11.5 million € led to a deceleration of the process to displacement velocities of some cm/year up to now. The houses and the road were not damaged.

After heavy rainfalls, a rock slide and a consecutive debris flow a mudslide comprising a volume between 3,5 and 5 million m3 was reactivated in Gschliefgraben valley (Gmunden, Upper Austria province) in 2007/2008. The mudslide moved downwards with displacement velocities of some metres per day, until it could be stopped finally. The geologic‐geotechnical model for the mudslide as well as the mechanisms and processes are described. They are influenced essentially by the pore water pressure and by the hydrostatic head. Comprehensive investigations showed that the clayey‐silty‐sandy‐pebbly masses in the Gschliefgraben are especially sensible to changes of water content and acting stresses. Based on these geologic‐geotechnical models for the movement process the mitigation measures carried out are described and their effects as well as their success are evaluated critically. Im Gschliefgraben (Gmunden, Oberösterreich) wurde nach starken Niederschlägen und einer Felsgleitung sowie einem anschließenden Murgang 2007/2008 ein Erd‐ und Schuttstrom mit einem Volumen zwischen 3,5 und 5 Mio. m3 wieder aktiviert. Dieser Erd‐ und Schuttstrom erreichte Bewegungsraten von mehreren Metern pro Tag, bis er schließlich gestoppt werden konnte. In dem Beitrag werden das geologisch‐geotechnische Modell für den Erd‐ und Schuttstrom sowie die Mechanismen und Prozesse aufgezeigt. Diese werden wesentlich vom Porenwasser‐ und Wasserdruck beeinflusst. Umfangreiche Untersuchungen haben ergeben, dass das Material ein besonders sensibles Verhalten gegenüber Änderungen des Wassergehalts und den auftretenden Spannungen hat. Aufbauend auf diesen geotechnisch‐geologischen Modellen für den Bewegungsprozess werden die durchgeführten Stabilisierungsmaßnahmen beschrieben und deren Wirkung kritisch untersucht. Darauf aufbauend wird deren Erfolg dargestellt und bewertet.

Abstract. Within the Northern Calcareous Alps fold-and-thrust belt of the Eastern Alps, multiple deformation phases have contributed to the structural grain that localised deformation at later stages. In particular, Jurassic rifting and opening of the Alpine Tethys led to the formation of extensional basins at the northern margin of the Apulian plate. Subsequent Cretaceous shortening within the Northern Calcareous Alps produced the enigmatic Achental structure, which forms a sigmoidal transition zone between two E-W striking major synclines. One of the major complexities of the Achental structure is that all structural elements are oblique to the Cretaceous direction of shortening. It was therefore proposed to be a result of forced folding at the boundaries of the Achental basin. This study analyses the structural evolution of the Achental structure through integrating field observations with crustal-scale physical analogue models, to elucidate the influence of pre-existing crustal heterogeneities on oblique basin inversion and the prerequisites for the formation of a sigmoidal hanging wall that outlines former basin margins. From brittle-ductile models, we infer that shortening oblique to pre-existing extensional faults can lead to the localisation of thrust faults at the existing structure within a single deformation phase. Prerequisites are 1) a weak basal décollement that is offset by an existing normal fault, 2) the presence of topography in the hinterland, 3) a thin-skinned deformation style. Consequently, the Achental low-angle thrust and corresponding folds was able to localise exactly at the basin margin, with a vergence opposite to the Jurassic normal fault, creating the characteristic sigmoidal morphology during a single phase of NW-directed shortening.