Ash fallout hazard from Irazú volcano, Costa Rica

The eruptive period between 1963-1965 at Irazu volcano showed that Costa Rica is highly vulnerable to ash fallout. Ash was carried by wind currents to-wards the Great Metropolitan Area (GMA), southwest to the summit, which contains about 60% of the national population. Previous work on hazard as-sessment for ash fall at Irazu only estimate influence areas without detailing hazard levels based on the observed distribution of events between 1963-1965. These cartographic models are not suited for realistic risk estimation, informed land use planning or proper emergency management. In this paper, we used the computer code NG-TEPHRA for simulating ash fallout from Irazu volcano, as-sessing the associated volcanic hazard and developing an improved hazard map from ash fall by devising a hazard index that combines the spatial probabilities of relevant scenarios with estimates of deposited ash volumes. Previous simula-tions results from our group were already calibrated against observed historical and field (geological) data from the 1963-1965 eruptive period and were used for obtaining the final hazard map. Our results represent a contribution for land use planning and emergency management purposes based on the application of computer models and interdisciplinary research towards numerically informed hazard models.