CONICET | Buscador de Institutos y Recursos Humanos

Modelling tephra fallout is a key task for modern volcanology as tephra dispersion severely impacts on humanactivities, infrastructure and environment.We used two particle-tracking numerical models to forecast tephra transport and fallout during the 3 March 2015eruption of Villarrica volcano (39°25S, 71°57 W). Lava fountain episode (1.5 km height above the crater level, a.c.l.)developed a sustained column of 10.8 km height a.c.l. by 16 minutes. Basaltic andesite tephra (~1.4 x 109 kg) wasdispersed to the southeast in a narrow, elongated area (Romero et al., 2018).In Model 1 (advection-diffusion), we assume that Rayleigh drag (drag force proportional to velocity squared) andgravity are the only relevant forces, because of the coarse particle sizes and large Reynolds number. We inform themodel with atmospheric wind and density structure from a Global Forecast System model of the time of eruption.Our results show that deposit geometry with cross-wind particle size grading can be explained well by the strongwinds and significant wind shear during eruption. These results show good agreement with field observations.Model 2 (ATLAS, Reckziegel et al., 2016; advection-diffusion-sedimentation) uses Weather Research and Forecasting(WRF/ARW) model (horizontal resolution of 0.25°). Density factor of particles was 0.6, lineal density to 61-107 g/cm3and eruptive parameters from Romero et al. (2018). Column height had a vertical distribution according to Suzuki.Due to lack of total grain size distribution (TGSD), the 12-13 January 2011 Etna eruption TGSD was used (Andronicoet al., 2014). Ash plume dispersal was confronted to GOES 13 satellite images, showing good agreement. Tephraloads (kg/m2) had good fit with field data, but modeled thickness was limited by meteorological data resolution.Further modelling should provide solution for short-lived and small-size eruptions within low meteorological dataresolution.