The impact of Mt. Etna's ash plume on the chemical composition of meteoric deposition

Abstract

Mt. Etna, in eastern coast of Sicily (Italy), is one of the most active and most intensely monitored volcanoes of the planet. It is the biggest volcanic point source of volcanic gases and particles to the troposphere in the Mediterranean basin. On the morning of December 24th 2018, a new lateral eruption of the Mount Etna started. This eruption was related to an intrusion of a magmatic dike on the high eastern flank of the volcano, which a two kilometers long fracture in the NNW - SSE direction. At the same time, the summit craters also produced a continuous strombolian activity generating a very dense dark ash plume, dispersed by the wind into the southeastern direction. This volcanic event well record from the atmospheric precipitations. During the period from June 2018 to May 2019, atmospheric precipitations were collected in the area of Priolo, eighty kilometer far SSE from Mt. Etna. The sampling and analytical protocols were chosen following the guidelines published by the main international agency involved in the monitoring of atmospheric precipitation. The rain gauges were open during the entire exposure time, collecting both wet and dry deposition (bulk collectors). All the collected water samples were analysed for major ion contents and for a large number of trace elements. The atmospheric precipitation of the period straddling the eruptive event is characterized by high concentration of major ions, such as Fluoride (up to 0.88 mg/l), Chloride (up to 124 mg/l) and Sulphate (23.1 mg/l). These derive mainly from the emitted volcanic gases (HF, HCl and SO2). On the another hand, an enrichment of some trace elements is also presented, such as Aluminum (up to 152 μg/l), Thallium (0.16 μg/l), Tellurium (0.025 μg/l). While Tl and Te are highly volatile elements typically enriched in volcanic emissions, Al is a refractory element that is probably correlated to the dissolution of the emitted volcanic ashes.