The efficacy of high frequency petrological investigation at open-conduit volcanoes: The case of May 11 2019 explosions at southwestern and northeastern craters of Stromboli

Typically, petrological monitoring studies focus on comparing eruptive phenomena with textural and compositional features of eruptive products recovered over the long term (days to years). In this contribution we present a high spatial (individual eruptive centers) and high temporal (minutes to hours) resolution petrological and volcanological investigation using as test site Stromboli volcano. On May 11 2019, we had the rare opportunity to collect individual fresh fallout ash products from eighteen consecutive explosions, and at the same time, to acquire continuous high frequency (50 Hz) infrared thermal data. We observe that explosions were more frequent and ash-dominated at the southwestern crater area (SCA, 8–10 events/hour) than at the northeastern crater area (NCA, 3–5 events/hour), where coarser material was ejected. The statistical analysis of glass and plagioclase compositions reveals differences in the products erupted from the two crater areas. SCA explosions tapped less differentiated magmas in equilibrium with more anorthitic plagioclase cores (An_~72–88), whereas NCA area explosions are more differentiated and in equilibrium with less anorthitic plagioclase cores (An_~68–82). Thermometric calculations based on clinopyroxene-plagioclase-melt equilibria highlight that NCA eruptions were fed by a colder magma relative to that feeding SCA eruptions. Diffusion modeling of Li concentration profiles in plagioclase also indicates longer timescales of magma degassing and ascent for NCA eruptions, leading to preferential groundmass crystallization at the conduit walls and transition from sideromelane to tachylite textures. The final emerging picture is that concurrent eruptions from distinct vent areas at Stromboli are heralds of distinct magma differentiation conditions within the uppermost part of the storage region, in close agreement with the observed eruptive phenomena. This high-resolution approach has the potential to unequivocally constrain the processes driving transient, rapid, explosive eruptions in active volcanoes, thus offering new insights on the complex interplay between magma dynamics, magma ascent rate, and eruptive behavior.