Leachate analyses of volcanic ashes from Stromboli volcano: A proxy for the volcanic gas plume composition?

Abstract

Many volcanoes show a change in chemical composition of the gas phase prior to periods of eruptive activity. Fine‐grained tephra erupted from active vents and transported through volcanic plumes can adsorb, and therefore rapidly scavenge, volatile elements such as sulfur, halogens, and metal species in the form of soluble salts adhering to ash surfaces. Analysis of such water‐soluble surface materials is a suitable supplement for remote monitoring of volcanic gases at inaccessible volcanoes. In this work, ash samples of the 2004 to 2009 eruptive activity of Stromboli volcano were sampled, leached, and analyzed for major and trace elements. Data analysis and interpretation was focused on determining the relationship between chemical composition of water‐soluble components adhering to volcanic ash and the volcano’s activity state. First results show significant temporal variations in ash leachate compositions, reflecting changes in the eruptive style of the volcano. In particular, we reveal that ash leachates S/F and Mg/Na ratios showed marked increases prior to a large‐scale explosion on 15 March 2007.