Long-term hazard assessment at Irazú volcano (Costa Rica)

Irazú volcano in Costa Rica is one of the most active and potentially dangerous volcanoes in Central America. Over the last 2600 years (before 1723 CE) it has experienced at least thirty explosive events of Strombolian, phreatomagmatic, and phreatic character and from different vent areas, ranging in size from VEI 1 to VEI 3, generating lava flows, lahars, non-eruptive sector collapses, and strong seismicity, even without eruptions. Recent tephrochronological data confirm that this volcano has had an eruption frequency ranging from 23 to 100 years, with a major event every 85 years. Several thousands of people live in the vicinity of the Irazú volcano, in areas that may be heavily impacted by lahars, ash falls, and pyroclastic density currents. Moreover, >2.5 million people live in the Greater Metropolitan Area, at the heart of the Costa Rica economy, located <30 km to the west of the volcano subject to the prevalent wind direction that has controlled ash fall emplacement for historical eruptions. In this contribution we conduct a long-term hazard assessment that aims to anticipate when (temporal analysis), where (volcanic susceptibility, i.e., vent location), and how (eruption scenarios) the next explosive episodes at Irazú volcano will occur. This information is essential to implement more rational territorial planning and to design better emergency plans for coping with future volcanic crises.