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Abstract:
Stromboli is well-known for its persistent, low-intensity, ordinary activity, occasionally interrupted by more violent, paroxysmal events and intermediate-scale major explosions. While the feeding system of ordinary and paroxysmal activity is largely discussed in the literature, key parameters such as magmatic source, pre-eruptive dynamics and the associated timescales remain elusive for major explosions. This information, however, is fundamental for identifying potential precursory signals and improving existing early-warning systems as well as understanding the processes that control variable eruption magnitude and intensity at open-conduit basaltic volcanoes. The 19 July 2020 eruption ejected an important amount of juvenile, deep-sourced magma providing an excellent opportunity to investigate the role of the deep feeding system activated during high-intensity activity. While geophysical parameters place this eruption at the upper limit of major explosions, similar to small-scale 2003 and 2007 paroxysms, a detailed geochemical characterisation of melt inclusions, olivine and matrix glass integrated with gas measurements highlights important differences in the feeding system dynamics. Melt inclusion volatile contents suggest a ponding zone at ⁓9.5 km b.s.l. and the activation of a shallower zone at ⁓5–6 km b.s.l.. Pre-eruptive magma and degassing dynamics appear to be controlled by deep CO2 fluxing and magma self-mixing. Olivine Fe-Mg diffusion modelling yields time constraints that are coherent with a change in CO2/SO2 ratios observed in the degassing plume, indicating a system perturbation ⁓20–25 days before eruption onset. The presented geochemical-petrological datasets, integrated with monitoring observations, provide a comprehensive framework for discussing the steady-state processes crucial for eruption forecast modelling.
