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We combined literature and experimental data to determine the role of magma mixing in the pre-eruptive dynamics of the Aeolian Islands volcanoes. As a first step, we systematically reviewed the evidence supporting the hypothesis of mixing-triggered eruptions in the Aeolian archipelago, providing textural, chemical, and rheological constraints. The existing data highlighted the significant role of magma mixing in many eruptions within the Aeolian archipelago. Examples include the Upper Pollara and Porri volcano eruptions at Salina, Monte Guardia, and the AD 1230 Monte Pilato eruption at Lipari, as well as the present-day activity at Stromboli. Then, we focused on Vulcano Island, chosen as a case study because it represents one of the volcanoes posing the highest risk in the Aeolian archipelago. At Vulcano Island, we highlighted the role of magma mixing in the AD 1739 and 1888–90 eruptions. Finally, we investigated mixing-to-eruption timescales for the AD 1739 eruption, performing mixing experiments, and evaluated the progressive decay of the chemical concentration variance with time. Results pointed to mixing-to-eruption timescales of the order of 29 ± 9 h and magma ascent rates ranging between 3×10−2 and 5×10−2 m s−1. We finally emphasized that the presented results may have significant implications in the context of volcanic hazard mitigation and planning of emergency activities.

The Campi Flegrei caldera (southern Italy) is one of the most hazardous volcanic systems on Earth, having produced >60 eruptions in the past 15 ka. The caldera remains active and its potential for future eruptions is high, posing a danger to the dense population living nearby. Despite this, our understanding of pre-eruptive processes and the architecture of the sub-volcanic system are poorly constrained. Here, we combine established petrological techniques, geothermobarometric evaluation, and high-resolution trace element crystal mapping, to present a multifaceted, coherent reconstruction of the complex pre-eruptive dynamics and eruption timescales of Astroni volcano located in the eastern sector of Campi Flegrei caldera. The Astroni volcano is an important case study for investigating plumbing system processes and dynamics at Campi Flegrei caldera because it produced the most recent (ca. 4 ka ago) Plinian eruption within the caldera (Astroni 6); current long-term forecasting studies postulate that a similar sized event in this location is a probable future scenario. Geothermobarometric results indicate interaction between an evolved, shallow magma chamber, and a less evolved, deeper pocket of magma, in agreement with previous studies focused on the Astroni 6 eruption products. In addition, a range of textural and trace element zoning patterns point to a complex evolution of both magmas prior to their subsequent interaction. High-resolution trace element crystal maps reveal discrete zonations in compatible elements. These zonations, combined with knowledge of K-feldspar growth rates, highlight a recharge event in the shallow plumbing system a few hours to days before the Astroni 6 eruption.

The Santa Bárbara trachytic eruption (~ 16 ka) was one of the major eruptions of the Sete Cidades Volcano (São Miguel Island, Azores), recording the last phase of caldera formation. Here, we report and combine geochemical, mineralogical, and petrological constraints on natural samples with time-series experiments to describe the pre-eruptive conditions of the Santa Bárbara plumbing system. The trachytic pumice clasts are notably characterized by the presence of hawaiitic enclaves, banded textures (~ 60-67 wt% SiO ) and high variability in mineral phases, occasionally rounded and partially resorbed. The hawaiitic enclaves contain quench textures such as sharp contacts with the trachytic groundmass, as well as acicular and skeletal growth of several minerals, pointing to a high-temperature gradient between the hot hawaiitic magma and the colder trachytic reservoir. Distinct phenocryst rim compositions in both magmas exclude significant chemical diffusion. We suggest that the hawaiitic enclaves represent an intrusion that triggered the eruption, but was only partially involved in the mixing process that generated the banded groundmass textures. These textural heterogeneities are interpreted to be related to a self-mixing event induced by convection within a compositionally zoned reservoir, with trachytic and mugearitic magmas at the top and the bottom, respectively. In detail, the model requires the likely arrival of hawaiitic magma to the base of the reservoir, inducing mixing by reheating of the resident mugearitic magma and volatile transfer. These processes produced a thermo-chemical destabilization (i.e., convection) of the shallow reservoir and mixing between the mugearitic and the trachytic magmas. We reproduced the observed chemical signatures performing time-series mixing experiments and calculated the concentration variance decay during mixing. Estimated timescales indicate that the hawaiitic intrusion took place ~ 41 h before the onset of the eruption.