Mobility and hazard analysis of selected landslides in Lower Austria

Landslide processes often cause great economic losses, infrastructure damage and numerous casualties in many mountains and hilly landscapes worldwide. Landslide processes are very diverse, and may be shallow or deep, slow, or fast, with translational or rotational movements, and can sometimes even have a compound nature, with a single event behaving in different ways along time or space. For example, under certain conditions, slow-moving landslides can increase their speed, becoming flows with a large mobility range and destructive energy.

Although the methods for creating landslide susceptibility and hazard maps are now well advanced, they often do not represent the diversity of the landslide processes. Moreover, they do not represent hazard to the different stages of land sliding sub-processes, like failure, movement, and deposition area. Even though these sub-processes are connected, the final outcome of a disastrous event can differ greatly according to the movement mechanisms and pre-event conditions. This way, reliable hazard maps for single landslides, that account for their changing behavior during motion, still faces significant challenges.

The core purpose of this research is to evaluate the mobility and hazard scenarios of three slow-moving landslides with varying extensions, depths, and topography. All the study areas are located in Lower Austria. The run-out of the landslides was estimated using r.avaflow, a physically based mass flow model. The depth and soil structure of the landslides has been previously investigated by geotechnical and geophysical analysis. Different scenarios were considered for the modelling, including different factors like landslide extent, soil depth, and assumed water saturation, that determines the flow velocity, extent, and viscosity and thus the spatial extent of the run-out. The temporal probability of failures was analyzed using a physically based slope stability model. Using rainfall, snow, and temperature records from nearby gauging stations in Lower Austria, each landslide event was linked to different triggering rainfall or snowmelt events, and the slope stability was evaluated in terms of their Safety Factor.

The output of the analysis is a set of different landslide run-out maps for each of the three study areas. These maps also include the temporal probabilities for each landslide, considering several extent and mobility scenarios. The results support the decision-making policies, including risk reduction measures, and the implementation of landslide early warning systems.