Conception of a method for the creation of volcanic risk index maps from the case study of the Chaine des Puys and the agglomeration of Clermont-Ferrand, France
Bion, Pascale Marie-Pierre
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Risk index maps are variants of risk maps. They contain unique kinds of information - relative levels of risk - and can therefore be a more effective communication tool than traditional risk maps. Despite their apparent simplicity, their production is the result of a complex risk analysis, requiring the consideration of multidisciplinary indicators, expressing different parameters of the physical and human dimensions of the environment and their interactions. The risk index is obtained by the combination of hazard and vulnerability data. As of now, no complete methodology has been conceived to quantify volcanic risk. The methodology developed here proposes a framework to assess risk levels in regions potentially impacted by volcanic hazards. It is based on the case study of the Chaîne des Puys in France, a volcanic field dormant for around 5,000 years located less than 10 km to the West of the agglomeration of Clermont-Ferrand. The approach incorporates highly simplified volcanic hazard specificities and integrates a diversity of urban components to assess vulnerability. It also considers a temporal variability of the events and their direct associated effects. The method is simple and tends to be general in defining the essential elements to consider and the manner to combine them to obtain a risk value. It is also flexible in giving the possibility to include more detailed modeling and new data in the framework (allowing quick updates from the growth of knowledge on hazards and vulnerability in the area studied), but also in being adaptable to different kinds of environment and to different scales. Limitations of the method and ways to improve it have been considered. The use of GIS software turns out to be essential to combine the information but also to automate the volcanic risk index calculations. This project has also highlighted a lack of data on the Chaîne des Puys to define the volcanic hazards associated. The developed approach is aimed at urban planners, who would possess a new fundamental tool for organizing the territories located "nearby" volcanoes, in which population density is continually increasing. A possible application of this evolving tool for crisis management is also envisaged.