Irazu volcano ash fall simulation using a modification of the tephra software/Simulacion de caida de ceniza del volcan Irazu aplicando el programa tephra modificado

This paper uses the Suzuki volcanic ash simulation model (Suzuki, 1983) to simulate volcanic ashfall in the tephra version TEPHRA (Connors, 1991). The modified TEPHRA volcanic ash simulation program has been used to develop computer simulations of volcanic ashfall produced by Irazu volcano, Costa Rica. The ability of the modified TEPHRA program to simulate volcanic ashfalls is tested by reproducing successfully the ash fall distribution of the best known eruptive episodes from the 1963-1965 active period. Additionally, the mass of accumulated ash during 52 simulations agrees very well with the ash isopachs deposited during the 1963-1965 active period and well with the distribution of ash isopachs deposited during the last 2600 years. We conclude that the modified TEPHRA program is suitable to prepare ash fall hazards maps for Irazu and other volcanoes, on the condition that there is good knowledge of their most likely eruptive characteristics and local wind direction. Key words: Ashfall, computer simulations, TEPHRA, hazards maps, risk scenarios, Irazu volcano. El presente trabajo utiliza el modelo de Suzuki (Suzuki, 1983) para simular la caida de ceniza volcanica en la version TEPHRA (Connors, 1991). El programa TEPHRA modificado es sometido a prueba al simular exitosamente la distribucion de ceniza de los eventos eruptivos mejor conocidos en el volcan Irazu, Costa Rica. Adicionalmente, la masa de ceniza acumulada por 52 simulaciones de diseno concuerda satisfactoriamente con la distribucion de las isopacas de la ceniza depositada durante el periodo 1963-65 del volcan Irazu y relativamente bien con la distribucion de isopacas de la ceniza depositada durante los ultimos 2600 anos de actividad. Esta situacion justifica la aplicacion del programa TEPHRA modificado en la elaboracion de mapas de amenaza por caida de ceniza para el Volcan Irazu y otros volcanes en los cuales se tenga apropiada informacion sobre direccion del viento y caracteristicas eruptivas mas probables de presentarse en el volcan. Palabras Clave: Caida de ceniza, simulacion computacional, mapas de amenaza, TEPHRA, escenarios de riesgo, Volcan Irazu.