Abstract: The prevention of natural risks in mountainous areas: snow avalanches and debris-flows, requires more and more complex numerical simulations. These require to take into account the behaviour of complex materials as well as delicate numerical methods. These simulations provide after several hours or days of computation large quantities of data. The last step of the process is to communicate such results to the public and people in charge of political decisions. Considering the tools of decision making in the framework of natural risks in mountainous areas is still hardly accessible to non-specialists, we have initiated a research project whose goal is to use the generation of synthetic images to improve the level of possible communication of existing numerical tools. In practice, the goal of this research is to develop a series of tools making possible to go through from the simulation of natural risks to their graphically realistic representation. After a short presentation of numerical models, we present in details the work carried out to improve the structure of computation mesh according to the topography in order to make computations faster and more accurate, to validate models in the field by comparison to real events and to build a graphically realistic representation of the flows.