Reconstructing volcanic plume evolution integrating satellite andground-based data: Application to the 23rd November 2013 Etna eruption

Abstract

Recent explosive volcanic eruptions recorded worldwide (e.g. Hekla in 2000, Eyjafjallajökull in 2010, Cordón-15 Caulle in 2011) demonstrated the necessity of a better assessment of the Eruption Source Parameters (ESP; e.g. column height, mass eruption rate, eruption duration, and Total Grain-Size Distribution – TGSD) to reduce the uncertainties associated with the far-travelling airborne ash mass. Volcanological studies started to integrate observations to use more realistic numerical inputs, crucial for taking robust volcanic risk mitigation actions. On 23rd November 2013, Etna volcano (Italy) erupted producing a 10-km height plume, from which two volcanic clouds were observed at different altitudes from 20 satellite (SEVIRI, MODIS). One was retrieved as mainly composed by very fine ash (i.e. PM20), whereas the second one as made of ice/SO2 droplets (i.e. not measurable in terms of ash mass). Atypical north-easterly wind direction transported the tephra from Etna towards the Calabria and Puglia regions (southern Italy), permitting tephra sampling in proximal (i.e. ~5-25 km from source), and medial areas (i.e. Calabria region, ~160km). A primary TGSD was derived from the field measurement analysis, but the paucity of data (especially related to the fine ash fraction) prevented it from being entirely representative of 25 the initial magma fragmentation. For better constraining the TGSD assessment, we also estimated the distribution from the X-band weather radar data. We integrated the field and radar-derived TGSDs by inverting the relative weighting averages to best-fit the tephra loading measurements. The resulting TGSD is used as input for the FALL3D tephra dispersal model to reconstruct the whole tephra loading. Furthermore, we empirically modified the integrated TGSD by enriching the PM20 classes until the numerical results were able to reproduce the airborne ash mass retrieved from satellite data. The resulting 30 TGSD is inverted best-fitting the field, ground-based, and satellite-based measurements. The results indicate a total erupted mass of 1.2 × 10^9 kg, being similar to the field-derived value of 1.3 × 10^9 kg, and an initial PM20 fraction between 3.6 and 9.0 wt%, constituting the tail of the TGSD.