Risk scenarios for a future eruption in the Chichinautzin monogenetic volcanic field, South México City

The Chichinautzin Monogenetic Volcanic Field creates volcanic risks for México City. To evaluate the possible effects and economic impacts of a future eruption, three scenarios based-on the spatial distribution of the most recent eruptions and the study of their characteristic are proposed. Scenario A, a Violent Strombolian eruption at the northwestern edge of the volcanic field, with eruptive columns 6-8 km high and emission of low-viscosity lava flows. Scenario B, Santiaguito-type eruption, a thick, high-viscosity lava flow that generates rock falls and short Merapi-type pyroclastic flows in the central northern area. Scenario C, a Hawaiian to Strombolian eruption with eruptive columns <6 km high and the emission of low viscosity lavas in the central part of the field. From these scenarios, numerical simulations of lava and tephra were carried out to obtain conditional hazard maps. The risk evaluation integrates the analysis of hazard, exposure, vulnerabilities, resilience, and the estimation of the costs of possible damages with physical and sociodemographic indicators available at the city block level, including rural areas. Two vulnerability curves were integrated for housing, the first for lava flows, which considers that a thickness >= 2 m of lava causes total loss (considering the loss of the function and accessibility); and a second curve for tephra that considers that an accumulated thickness in dry conditions of 20 cm of tephra produces generalized damage to all type of houses. By combining the vulnerability and hazard maps, two risk maps were constructed, one for lava flows and the other for tephra. The total direct cost of the expected damages was calculated for each scenario considering the cadastral value of the land and buildings for each property at risk. The costs for the most probable and the most catastrophic scenario amount to >14 billion US dollars, equivalent to 1.2% of the national GDP. Mitigation measures, mainly of the non-structural type are proposed.