Debris flows and lahars are multi-phase mixtures made of variable amounts and types of sediment and water. They can be triggered by a variety of processes, like the interaction of explosive volcanic eruptions with a source of water (e.g. crater lake or a glacier), prolonged and intense rainfall remobilizing loose sediments among others. They flow downslope due to gravity and are characterized by a high bulk density and complex particle interactions which explain their capability of transporting large blocks and debris and exerting significant dynamic impact on building and infrastructures.The intrinsic complexity of the physical processes taking place in these flows has been addressed through different approaches with little or no interaction between them. These include fieldwork, real-time measurements (monitoring), experiments (from laboratory to large scale) and numerical modelling. Bringing them together has the potential to lead to a better understanding of the fluid dynamics and eventually improving the constitutive equations and initial and boundary conditions required for predictive simulations. Simulation tools, in turn, are fundamental for assessing the hazard related to these processes. In this session we welcome contributions presenting results from applications of the different approaches described above. We particularly encourage multidisciplinary contributions, e.g. combination of experiments and modelling or exposure and vulnerability analyses for risk assessment. To integrate and discuss multiple sources of information will summarize the challenges still needed in improving our current knowledge of these phenomena and will extend networks focused on designing new and more accurate models for hazard assessment and mitigation strategies.

Core connection between the proposed session and societal risk mitigation:Understanding the physics of debris flows and lahars is of paramount importance for improving our capability to predict the impact of these flows on the environment and human society and then mitigate their hazard.