Rapid mass movement hazards in mountains such as snow avalanches, mountain rivers floods, rockfalls but also landslides, floods put humans and property at risk with dramatic consequences. Risk reduction is achieved through structural measures (e.g. dams, dikes, protective nets...) and non-structural measures such as zoning control maps, contingency plans, preventive information... The risk management process involves several temporal steps (preparedness, mitigation, crisis management, recovery...) and concern spatial zones (triggering, propagation and deposition or extension areas). Those steps imply as many decisions for the experts, the risk managers, the local authorities... This talk focuses on the existing links between information imperfection, expert assessment and internal (technically based) decision as a common feature of the european projects PARAMount and MONITOR II .