Preliminary investigation into temporal variation of volcanic ash adherent water-soluble components at Stromboli volcano during 2004-2009 eruptive activity

A change in the chemical compositions of volcanic gases is one of the noticeable phenomena that frequently occurs prior to an eruption. Tephra in plumes can absorb and thereby rapidly deposit volatiles including sulphur, halogen and metal species. These may then be leached (e.g. by rainfall), potentially releasing heavy loads into soils and water bodies. Their analysis is a suitable supplement for remote monitoring of volcanic gases from inaccessible volcanoes. Freshly fallen ashes of the eruptive activity from 2004 to 2009 at Stromboli volcano were sampled, leached and analysed for major and trace elements. This study is aimed at determining the causes of the compositional variations of the ash adherent water-soluble components with plume composition. In the work the literature on volcanic ash-leachates is also summarised and compared to the different worldwide volcanoes in terms of components adhering to the ash. First results on ash-leachates at Stromboli show temporal variations in the Cl/S and Cl/F ratios, reflecting changes in the eruptive style. Furthermore, ash-leachates might suggest the occurrence of impending paroxysmal events. Data from trace metals evidence that ash surfaces are enriched in the more volatile elements (i.e. Se, Cd, Cu, Pb) resulting from plume adsorption.