The 2002-03 Etna explosive activity: Tephra dispersal and features of the deposits

The onset of Mt. Etna's 2002-03 eruption was marked by intense explosive activity beginning on 27 October 2002 and persisting until 30 December. This phase of activity produced abundant ash emission that impacted the local economy and air traffic. Thereafter, explosive activity declined with the eruption ceasing on 28 January 2003. In this paper, we present field data collected during the eruption and use these to obtain input data for tephra dispersal model. This was applied, after validation, to extrapolate the total distribution of the deposits emplaced during the explosive activity. Detailed sampling of fallout deposits was completed on 27, 28, 31 October and 4 November. This enabled construction of isomass maps and calculation of the erupted mass. Grain-size analysis of all collected samples was used to reconstruct the total grain-size distribution which displays a peak at 0.5 Phi. Column height was estimated at 3.3-7 km by combining barometrical altimeter data during over-flights with the analysis of images and videos. This was used to estimate a total erupted mass of 4.4 +/- 0.6 x 10(10) kg. Simulations showed that the deposit was significantly affected by variations in wind direction and mass eruption rate, with deposits being dispersed mainly on the E sector of the volcano due to a dominant easterly wind. Our study underlines that basaltic volcanoes, such as Etna, can produce huge amounts of ash, as well as lava, and that an improvement in the knowledge of dispersal processes during prolonged explosive activity is required to better mitigate the associated hazards.