Validation of the FALL3D model for the 2008 Chaiten eruption using field and satellite data

Abstract

The 2008 Chaitén Volcano eruption began on 2 May 2008 with an explosive phase that injected large amounts of tephra into the atmosphere. During the first week of the eruption, volcanic ash clouds were transported for hundreds of kilometres over Argentina by the prevailing westerly winds. Tephra deposition extended to the Atlantic Ocean and severely affected the Argentinean Patagonia. Impacts included air and water quality degradation, disruption of ground transportation systems and cancellation of flights at airports more than 1,500 km apart. We use the FALL3D tephra transport model coupled with the Weather Research and Forecasting-Advanced Research Weather (WRF-ARW) meteorological model to simulate tephra fall from the 2-9 May 2008 eruptive period. Our hindcast results are in good agreement with satellite imagery and reproduce ground deposit observations. Key aspects of our analysis, not considered during syn-eruptive forecasts, are the re-initialization of each simulation with actualized meteorological forecast cycles and better constrained model inputs including column heights (inferred from reanalysis of GOES-10 imagery and nearby atmospheric soundings) and granulometric data obtained from field campaigns. This study shows the potential of coupling WRF/ARW and FALL3D models for short-term forecast of volcanic ash clouds. Our results highlight that, in order to improve forecasting of ash cloud dispersion and tephra deposition, it is essential to implement an operational observation system to measure temporal variations of column height and granulometric characteristics of tephra particles in nearly real-time, at proximal as well as distal locations.