Abstract.As the amount of spatial data is growing, there is increased interest in developing tools to explore, visualize and interpret them, with the final aim of informing decision making efficiently. Within the European MIAVITA project, we examined this issue in the case of volcanic areas, where existing geospatial databases are particularly complex due to the number of threats to be considered, including volcanic (e.g. lava flows, ash fall) and non-volcanic hazards, such as landslides or tsunamis. We involved a group of hazard and risk analysts and managers, civil security officers, GIS analysts and system developers to design a Web-based geographical information system (WebGIS). We tested the system at the Mount Cameroon volcano, taking advantage of a complex hazard and risk geographical database. This study enabled identifying key requirements for such tools in volcanic areas, such as the need to manage user privileges differently according to their profile and the status of the volcano. This work also highlights that, in addition to the development of large geoinformation clearinghouses, there is a need for sitespecific information systems focused on working procedures of users, in order to fill the last gap between data producers and users.

Abstract. In volcanic areas exposed to multiple geological hazards, the efficient interpretation of the increasing amount of geographical data is a challenging issue. Within the European MIAVITA project, we investigated to which extent WebGIS can facilitate this interpretation through the visualization of such complex hazard and risk database. This analysis was structured around (1) the development of a Web-based Geographical Information System (WebGIS) and of an application for managing the geographical database, and (2) interactions with a group of hazard and risk analysts and managers, civil security officers, GIS analysts and system developers. We tested the system in the Mount Cameroon volcano, taking advantage of a complex hazard and risk geographical database collected previously. Key requirements here related to the need for a structured and flexible GIS-database and to manage user's privileges differently according to their profile and the status of the volcano. In addition, this study showed that it is important for such systems to manage different status for data, from data than can only be interpreted by experts (e.g. some complex remote sensing products) to data that can be disseminated to any potential user (e.g. a regulatory hazard map). While the developed tool is able to provide users with enough flexibility to respond to the users' requirements, it is still necessary to own expertise in WebGIS to manage such tools in the long term in local volcano observatory. Nevertheless, this study shows that WebGIS-based systems can relatively easily integrate some most important working procedures of hazard and risk management in volcanic areas.