Abstract. Gravitational natural hazards such as snow avalanches, rockfalls, shallow landslides and volcanic activity represent a risk factor for mountain communities around the world. In particular where documentary records about these processes are rare, decisions on risk management and land-use planning have to be based on a variety of other sources including vegetation and tree-ring data and natural hazard process models. We used a combination of these methods in order to evaluate dynamics of snow avalanches and other natural hazards at Valle de las Trancas, in the Biobío Region in Chile. Along this valley, natural hazards threaten not only the local human population, but also the numerous tourists attracted by outdoor recreational activities. Given the regional scarcity of documentary records, tree-ring methods were applied in order to reconstruct the local history of snow avalanches and debris flow events, which are the more important weather-related processes at respective tracks. A recent version of the model Rapid Mass MovementS (RAMMS), that includes influences of forest structure, was used to calculate different avalanche parameters such as runout distances and maximum pressures, taking into consideration the presence/absence of forest along the tracks as well as different modelled return periods. Our results show that local Nothofagus broadleaved forests contribute to a reduction of avalanche runout distances as well as impact pressures on present infrastructure, thus constituting a valuable ecosystem disaster risk reduction measure that can substitute or complement other traditional measures such as sheds.
OS-4 Risk Communication of Chemical Plant as Risk Reduction Measure