International audienceTo help improve the safety of its population faced with natural disasters, the Cameroon Government, with the support of the French Government, initiated a programme of geological risk analysis and mapping on Mount Cameroon. This active volcano is subject to a variety of hazards: volcanic eruptions, slope instability and earthquakes. Approximately 450,000 people live or work around this volcano, in an area which includes one of Cameroon's main economic resources. An original methodology was used for obtaining the information to reply to questions raised by the authorities. It involves several stages: identifying the different geological hazard components, defining each phenomenon's threat matrix by crossing intensity and frequency indices, mapping the hazards, listing and mapping the exposed elements, analysing their respective values in economic, functional and strategic terms, establishing typologies for the different element-at-risk groups and assessing their vulnerability to the various physical pressures produced by the hazard phenomena, and establishing risk maps for each of the major element-at-risk groups (population, infrastructures, vegetation, atmosphere). At the end of the study we were able (a) to identify the main critical points within the area, and (b) provide quantified orders of magnitude concerning the dimensions of the risk by producing a plausible eruption scenario. The results allowed us to put forward a number of recommendations to the Cameroon Government concerning risk prevention and management. The adopted approach corresponds to a first level of response to the authorities. Later developments should make it possible to refine the quality of the methodology

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. This paper presents an integrated approach to conduct a scenario-based volcanic risk assessment on a variety of exposed assets, such as residential buildings, cultivated areas, network infrastructures or individual strategic buildings. The focus is put on the simulation of scenarios, based on deterministic adverse event input, which are applied to the case study of an effusive eruption on the Mount Cameroon volcano, resulting in the damage estimation of the assets located in the area. The work is based on the recent advances in the field of seismic risk. A software for systemic risk scenario analysis developed within the FP7 project SYNER-G has been adapted to address the issue of volcanic risk. Most significant improvements include the addition of vulnerability models adapted to each kind of exposed element and the possibility to quantify the successive potential damages inflicted by a sequence of adverse events (e.g. lava flows, tephra fall, etc.). The use of an object-oriented architecture gives the opportunity to model and compute the physical damage of very disparate types of infrastructures under the same framework. Finally, while the risk scenario approach is limited to the assessment of the physical impact of adverse events, a specific focus on strategic infrastructures and a dialogue with stakeholders helps in evaluating the potential wider indirect consequences of an eruption.

Abstract. This paper presents an integrated approach to conduct a scenario-based volcanic risk assessment on a variety of exposed assets, such as residential buildings, cultivated areas, network infrastructures or individual strategic buildings. The focus is put on the simulation of scenarios, based on deterministic adverse events input, which are applied to the case-study of an effusive eruption on the Mount Cameroon volcano, resulting in the damage estimation of the assets located in the area. The work is based on the recent advances in the field of seismic risk. A software for systemic risk scenario analysis developed within the FP7 project SYNER-G has been adapted to address the issue of volcanic risk. Most significant improvements include the addition of vulnerability models adapted to each kind of exposed element and the possibility to quantify the successive potential damages inflicted by a sequence of adverse events (e.g. lava flows, tephra fall, etc.). The use of an object-oriented architecture gives the opportunity to model and compute the physical damage of very disparate types of infrastructures under the same framework. Finally, while the risk scenario approach is limited to the assessment of the physical impact of adverse events, a specific focus on strategic infrastructures and a dialogue with stakeholders helps in evaluating the potential wider indirect consequences of an eruption.

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.