Mapping hazard zones, rapid warning communication and understanding communities: primary ways to mitigate pyroclastic flow hazard

Abstract

Protection against the consequences of Pyroclastic Density Currents (PDCs) is almost impossible due to their high velocity, temperature, sediment load and mobility. PDCs therefore present a challenge for volcanic crisis management in that specific precautionary actions, essentially evacuations, are required to reduce loss of life. In terms of crisis communication for PDC hazards, there are three challenging questions that arise in terms of reducing risk to life, infrastructure and livelihoods. (1) How do we accurately communicate the hazardous zones related to potential PDC inundation? The areas exposed to PDC hazard are difficult to assess and to map. In terms of risk/crisis management, the areas considered at risk are usually those that were affected by PDCs during previous eruptive episodes (decades or centuries ago). In case of “larger-than-normal” eruptions, the underestimation of the hazard zone may lead to refusals to evacuate in the “newly” threatened area. Another difficulty in assessing the PDC hazard zones relate to their transport processes that allow surmounting of the topography and in some cases across the surface of water. Therefore warning systems must be able to cover vast areas in a minimum of time. (2) How do we efficiently warn people in time? PDCs are extremely mobile and fast. It is therefore necessary to raise the alert early enough before the onset of the first PDCs. A challenging question in terms of crisis communication is related to the type of tools used by the local authorities, modern and traditional tools both of which have advantages and disadvantages. (3) Why are people reluctant to evacuate? Local inhabitants can be reluctant to evacuate during a crisis if traditional warning signs or signals they are familiar with are lacking, if they don’t receive both traditional and official warning, and because they may lose their livelihoods. Thus a deeper understanding of the at‐risk communities and efficient dissemination of information are key issues in order to reduce vulnerability in PDC hazard regions.