’ response document Reconstructing volcanic plume evolution integrating satellite and ground-based data : Application to the 23 rd November 2013 Etna eruption

Recent explosive volcanic eruptions recorded from different volcanoes worldwide (e.g. Hekla in 2000, Eyjafjallajökull in 2010, Cordón-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. To do so, vVolcanological studies started to 20 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 satellite (SEVIRI, MODIS). One was described 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), 25 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 Based on the field data measurement analysis, we estimated the TGSD but the paucity of data (especially related to the fine ash fraction) prevented it from being entirely representative of the initial magma fragmentation. For better constraining the TGSD assessmentTo better estimate the TGSD covering the entire grain-size spectrum, we integrated the available field data with X-band weather radar and satellite retrievals. To assess the TGSD 30 associated with the 23rd November 2013 paroxysm (together with the other ESPs) , we firstalso estimated the grain-size distributions derived from i) field and ii)the X-band weather radar X-Radar data, respectively. Then, wWe integrated them field and radar-derived TGSDs by inverting the relative weighting averagesthe two distributions to best-fit the measured 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 resultingintegrated TGSD by enriching the PM20 classes 35 until the numerical results were able to reproduce the airborne ash mass retrieved from satellite data. The resulting TGSD is used as input for the FALL3D tephra dispersal numerical model to reconstruct the tephra loading and the far-travelling airborne ash mass. The optimal resulting TGSD is selected inverted by solving an inverse problem through a best-fitting with the field, ground-based, and satellite-based measurements. The results suggest suggestindicate a total erupted mass of 1.2 × 109 kg, which is verybeing similar to the field-derived value of 1.3 × 109 kg, alsoand an initial , and a TGSD with a PM20 40 fraction between 3.6 and 9.0 wt%, to use within constituting the tail of the TGSD..

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