Volcanic eruptions are commonly subdivided into effusive and explosive activity depending on conduit dynamics that can either result in the outflow of lava when the degassed magma reaches the surface (effusive eruptions), or in the fragmentation of magma at various depths (dry explosive eruptions, from Hawaiian to Ultra-Plinian, and wet explosive eruptions from Surtseyan to phreato-Plinian in the classification of Walker ( 1980)). Nonetheless, some

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A comprehensive understanding of the processes that occur during magmatic storage and pre-eruptive ascent—and of their associated timescales—is critical to identifying potential precursory signals, and to developing robust volcano early-warning systems. Stromboli’s persistent activity comprises continuous degassing and explosive activity that ranges from hourly, low-intensity “normal” activity to occasional, more violent, paroxysmal activity. While the magma source processes that drive normal and paroxysmal activity are reasonably constrained, eruptive activity intermediate in magnitude and intensity (i.e., major explosions) remains elusive in terms of classification, source region, and pre-eruptive timescales. Here, we investigate the 19 July 2020 major explosion that geophysical parameters place at the upper limit of the major explosions field, close to small-scale paroxysms such as the 2003 and 2007 events. The geochemical signatures of matrix glass, olivine, melt inclusions, and embayments—integrated with gas measurements—highlight important differences in eruption source, ascent behaviour, and pre-eruptive timescales of the studied event when compared to paroxysms. Melt inclusion volatile contents identify that magma rise begins from a slightly shallower source (~9.5 km below sea level, b.s.l.) than for paroxysms (11.4 km b.s.l.), with the activation of a shallower ponding zone at 5–6 km b.s.l.. This, in combination with intermediate matrix glass compositions, suggests complex ascent behaviour, characterised by CO2 buffering in the deep ponding region and magma self-mixing in the shallower zone. Fe–Mg-diffusion modelling in olivine indicates a system perturbation starting ~20–25 days before eruption onset, in agreement with the timescale of volcanic gas CO2/SO2 ratio changes observed in the plume, and significantly shorter than that observed prior to paroxysms (~4 months). The geochemical dataset provides insights into the processes controlling the steady-state conditions and the broad spectra in eruption magnitude and intensity at Stromboli and bears important implications for eruption forecasting.

<p>Between 19 September and 13 December 2021 (85 days), a flank eruption took place along the Cumbre Vieja ridge (La Palma Island), one of the most active volcanic centers of Canary Islands. The last 7000 years of Cumbre Vieja activity has been characterized by a combination of effusive and explosive eruptions. These generated both cinder cones and lava flows. The previous event occurred between October 26 and November 28, 1971 (eruption of Teneguía). The 2021 eruption was characterized by the alternate (and often simultaneous) emission of lava flows, lava fountains and tephra plumes along a ~1 km-length fissure consisting of about ten vents that built a cinder cone complex. The southern vents were mostly associated with the generation of tephra plumes and lava fountains, while the northern vents were mostly associated with the generation of lava flows. The ~12 km<sup>2</sup> lava flow field on the west side of the island reached the sea on September 28, forming a new lava delta and interacting with sea water producing lava haze (i.e. laze). Even though tephra was sedimented all over La Palma and sometimes reached the neighboring islands, the cumulative tephra deposit is mostly elongated towards the southwest and the northeast due to the prevailing wind direction, reaching a maximum thickness southwest of the fissure. Both lava fountains and more explosive tephra plumes contributed to the formation of the tephra deposit. Tephra plumes were associated with variable intensity reaching a few kilometers of altitude (<10 km). Multiple tephra layers, which are associated with distinct phases of the eruption, can be identified based on grainsize, clast texture and deposit characteristics. Some of the layers are dominated by black fluidal glassy clasts mostly associated with lava fountain activity, while some others are dominated by brown, finely to coarsely vesicular clasts mostly associated with more explosive tephra plumes. Most layers, as well as the cumulative deposit, are characterized by a thinning break-in-slope between 3-4 km from the vents. A distinctive lithic-rich, reddish layer, which mostly sedimented on October 15-16 during a new vent opening phase, helps the correlation among the various layers. Grainsize on land is dominated by lapilli and coarse ash, with fine ash being mostly deposited in the ocean (beyond 6 km from the vents). Individual layers are associated with volumes that range between Volcanic Explosivity Index (VEI) 2 and 3, while the total tephra deposit is associated with a VEI 3 (excluding the volume of the cone).</p>

The Baia-Fondi di Baia was a multi-stage, small-scale eruption which occurred in the western part of the Campi Flegrei caldera at 9525-9696 BP, marking the onset of Epoch 2 of post-Neapolitan Yellow Tuff volcanism. The eruption was characterized by a complex series of events related to two distinct eruptive episodes (Baia and Fondi di Baia) separated by a short time interval, and each characterized by several eruptive phases. Mineralogical, geochemical (major, and trace elements on whole-rocks, major and volatile elements on matrix glasses and melt inclusions) and Sr-isotope characterization of the tephra material sampled along the entire sequence was carried out in order to constrain magmatic evolution and dynamics of the feeding system. Three main compositional groups were identified in matrix glasses and interpreted as representative of different magma bodies: i) a trachyte (SiO2: 60.3-64.7 wt.%), which is volumetrically predominant; ii) a tephriphonolite-latite (SiO2: 55.1-57.9 wt.%); and iii) an intermediate magma group between phonolite and trachyte compositions. This wide compositional heterogeneity contrasts with the narrow variability recognized in the bulk-rock compositions, which are all trachytic. Mineral, melt inclusions and Sr-isotope data suggest that the trachytic magma possibly derived from the Campanian Ignimbrite reservoir located at 6-9 km depth.Volatile content in matrix glass indicates a storage depth of at least 6 km for the tephriphonolite-latitic magma. The intermediate magma is interpreted as being derived from a remelting and assimilation process of a partially crystallized trachytic body (crystal mush) by the hotter tephriphonolite-latitic magma. As the tephriphonolite-latite was erupted together with the trachyte from the beginning of the eruption, we suggest that the ascent of this magma played a fundamental role in triggering the eruption. Upwards through the tephra sequence, we observed a progressive increase of the tephriphonolite-Prepared for Bull Volc latitic and intermediate phonolite-trachytic components. The presence of banded clasts characterized by different compositions is also indicative of syn-eruptive mingling during the final phases of the eruption.