COLLECTIVE EVACUATION RULES AND UNFORESEEN RISK IN VOLCANIC DISASTERS

The decisions on the collective evacuation order by the mayor for the municipality's citizen faced with disaster crisis can be formulated as meta-decisions on changes in decision modes from the normal mode to the crisis one. Given deep uncertainty of disaster processes, the disaster mitigation plan prepared in advance can only provide a benchmarking scenario on how the local citizen and government respond to the probable disaster scenarios, which is to be shared commonly by the people concerned. However, during the crisis period when the disaster is actually processed, the mayor is highly required to judge whether the on-going disaster process can be maneuvered by the set of predetermined rules described in the plan, or not. If not, she shall implement the contingent emergency rule for the on-going unforeseen disaster process. This paper proposes a model for designing the benchmarking evacuation rule for volcanic disasters, which also enables to detect systematically extraordinary contingencies where exceptional evacuation rules are necessary. In addition, the proposed model is applied to the actual case of Mt. Usu in Hokkaido, Japan.