Volcanic ash forecast – application to the May 2008 Chaitén eruption

A Folch,O Jorba,J Viramonte

doi:10.5194/nhess-8-927-2008

Abstract

Abstract. We model the transport and subsequent deposition of ash from Chaitén volcano, Chile, during the first week of May 2008. The simulation couples the Weather Research and Forecasting (WRF) meteorological model with the FALL3D dispersion model. We only use semi-quantitative volcanological inputs based on the first eruption reports. We consider two different run types based on forecasted and hindcasted meteorological conditions. The first simulation type can be regarded as a syn-eruptive operational forecast for the 2–8 May period. We predict the evolution of the ash cloud position, the concentration of ash on air, the expected deposit thickness, and the ash accumulation rates at different localities. The comparison of model results with observed cloud arrival times and satellite images shows the goodness of the combined WRF+FALL3D forecast system and points out the feasibility of combining these two models for short-term forecast of volcanic clouds and ash fallout.

Highlights

Fallout of tephra following explosive volcanic eruptions threats the communities located around active volcanoes and beyond
The comparison of model results with observed cloud arrival times and satellite images shows the goodness of the combined Weather Research and Forecasting (WRF)+FALL3D forecast system and points out the feasibility of combining these two models for shortterm forecast of volcanic clouds and ash fallout
In the light of the above, the International Civil Aviation Organization (ICAO) promoted the creation of the Volcanic Ash Advisory Centers (VAACs) to keep pilots and international aviation industry informed of the location and movement of eventual volcanic ash clouds

Summary

Introduction

Fallout of tephra following explosive volcanic eruptions threats the communities located around active volcanoes and beyond. Large quantities of fine ash and aerosols injected into the atmosphere can remain air-borne from days to months and be transported by high level winds thousands of kilometers downwind Such fine particles affect the air quality and threat the aerial navigation causing drifting of aircraft routes to prevent degraded engine performance, loss of visibility, and possible failure of navigational instruments. Whenever there is an on-going eruption, the regional VAAC makes use of direct observations by pilots, satellite imagery, and modeling, to issue warning bulletins and to forecast the short-term evolution of the cloud. In this paper we use the recent Chaiten eruption, Chile, to test the operational capacity of the FALL3D Eulerian model (Costa et al, 2006; Folch et al, 2008) to forecast ash concentration on air and expected deposit load and thickness. It is important to point out that our goal is not to perform a detailed study of the Chaiten eruption but to use it as a blind test to confront short-term model predictions and semi-

Objectives

Results

Conclusion