Processes controlling the 2010 Eyjafjallajökull explosive eruption

To constrain the temporal evolution of the fluid‐magma system responsible for the 2010 Eyjafjallajökull eruption (20 March to 20 May, 2010, Southern Iceland), we investigated the volatile, major, trace element, and Sr‐Nd‐Pb isotopic compositions of bulk lapilli and ash samples representing different stages of the eruption. In addition, we analyzed ash leachates and volcanic plume‐derived aerosols sampled over Southern Europe in early May 2010. Available remote‐sensing data for the total mass of SO2 liberated in the 2010 eruption, together with data obtained in this study, suggest that the high explosivity of the 2010 sub‐plinian Eyjafjallajökull eruption was caused by saturation of the pre‐eruptive hybrid trachyandesitic magma with aqueous fluid. We hypothesize that the bulk of the aqueous fluid had been dissolved in the trachydacitic melt at least since the eruption of 1821–1823. The trachydacitic melt was enriched in volatiles, large‐ion lithophile elements, and high field strength elements, a composition similar to that of oceanic sediments. The Sr‐Nd‐Pb isotopic data obtained in this study, combined with existing O isotopic data on bulk 2010 Eyjafjallajökull lapilli and ashes, demonstrate that this melt enrichment was due to its primary source being hydrous oceanic lithosphere entrained in a deep mantle plume rather than shallow hydrothermally altered crust. The hypothesized strong crystal fractionation of plume‐derived mafic melts (crystallized fraction >90%) from an enriched mantle source can explain the observed high explosivity of silicic and hybrid Icelandic magmas, especially those of the southeastern volcanic zone (Eyjafjallajökull, Katla, and Hekla). Key Points Saturation of the pre‐eruptive hybrid trachyandesitic magma with aqueous fluid Enriched mantle source can explain the high explosivity Strong crystal fractionation of plume‐derived mafic melts