Simulation of cascading mass flows in GIS: progress and challenges

The aim of this work is to learn about the capacities, but also the challenges connected to the modelling of high-mountain landslide cascades with the software r.avaflow, a comprehensive open source mass flow simulation tool. Thereby we use six case studies in Peru, Switzerland, and Iceland. The investigated chains of flow-like landslides were successfully reproduced with the two-phase and three-phase models of r.avaflow. However, the input parameters had to be empirically optimized for each single event in order to bring the model results in line with the observations. The use of such optimized parameter sets to events of different magnitudes remains a challenge. This is particularly important where threshold effects are involved. It limits the reliability of forward simulations for risk management. More back-calculated events would be required to derive guiding parameter sets which can be used for forward simulations. Further, equifinality issues and remaining uncertainties have to be considered. Therefore, parameter ranges and scenarios should be used instead sets of fixed parameter values. The resulting blurry information is less likely to be off target than sharp information, but less straightforward to interpret and to communicate to stakeholders. Besides additional parameterization and testing efforts, in the future r.avaflow should be extended by including the possibility to consider block sliding and flow transformations, and by interfaces with models for other processes (such as rock fall) and landslide initiation.