Tephra fallout hazard assessment at Tacaná volcano (Mexico)

Abstract

Tacaná volcano is one of the dormant volcanoes in Mexico. Its activity is demonstrated by recent phreatic explosions occurred in 1949 and 1986. At least four Plinian to sub Plinian eruptions have been recorded in the eruptive history of this volcano, which produced pumice and ash deposits that blanketed a vast area straddling the Mexican and Guatemalan territory. Currently, there is no quantitative tephra hazard study of the volcano fallout deposits nor of the dispersion of ash in the atmosphere.In this work, we present the first probabilistic tephra hazard assessment for the Tacaná volcano. Probabilistic hazard maps were computed both, for the tephra deposit, and for critical thresholds of airborne ash concentration at different flight levels. The FALL3D numerical model was used to perform hazard maps for a Plinian scenario defined on the basis of the Sibinal Pumice eruption occurred ∼23.5 kyrs ago, which is the most studied deposit of this type in the volcano's surroundings, even when just few of their most distal outcrops are preserved. Results of this work show that at ground level, the disturbance for this type of hazard would affect mainly Guatemalan territory and the state of Chiapas in Mexico. It could cause serious repercussions on the economy of the region, which is characterized mainly by cocoa, coffee and banana plantations. The ash dispersion into the atmosphere could disturb the airspace and major airports in Mexican territory and neighboring countries. In fact, probability ash dispersal maps show that the level of affectation to the air traffic would involve the possible closure of at least 23 airports in Mexico, Guatemala, Belize, Honduras, El Salvador and Nicaragua. Another collateral damage would be the remobilization of ash by lahars considering the near 4000 mm of rain in average poured yearly in the Soconusco region that would increase the sediment load of the Coatán and Suchiate rivers, and then could produce a severe damage to the lowlands, which in the case of the Mexican territory, is the most populated one.