Paroxysms at Stromboli Volcano (Italy): Source, Genesis and Dynamics

Abstract

Deciphering the triggering mechanisms of violent explosive activity is of broad interest for understanding the dynamics of basaltic open-vent volcanic systems. For nearly 1300 years Stromboli has been renowned not only for its continuous degassing activity and mild explosions at the summit craters, but also for short-lived, violent explosive events of variable scale, known as major explosions and paroxysms. Here, we focus on the 1456 and 1930 paroxysms and on the most recent events, in July and August 2019 at Stromboli. We show that shallow phenomena such as flank collapse, lava outpouring through fractures opening, or partial emptying of the shallow conduit, only speed up volatile-rich magma ascent by increasing the decompression rate, whereas pressurization of the crustal system and the deep refilling by magma and its CO2-rich gas phase play a major role in triggering paroxysms. Moreover, we present new data on the geochemistry of the 2019 bulk pumice, along with a compilation of data from the literature, chemical profiles in olivine crystals, and the physical parameters of explosive eruptions of wide ranging magnitude and intensity. For small and large paroxysms, timescales were derived from Fe–Mg diffusion profiles in olivine. In both types of explosion, the last phases of crystallization-diffusion indicate rapid magma ascent rates of two to ten days prior to eruption. Trace element concentrations (Nb, La and Ba) and ratios (Rb/Th) indicate that the 2019 pumice samples plot in the domain of magma batches erupted within the last 20 years at Stromboli. As a whole, there is no correlation between magma geochemistry and magnitude or intensity of explosive eruptions, which span a range of ∼3 orders of magnitude (from major explosions to large paroxysms) based on estimates of erupted tephra volumes. In contrast, olivine compositions are a good proxy for erupted tephra volumes and magma flux. The correlation among physical and chemical parameters, which is valid for the overall spectrum of eruptions, implies that the magmatic source ultimately controls eruptive dynamics.

Unoccupied Aircraft Systems (UASs) Reveal the Morphological Changes at Stromboli Volcano (Italy) before, between, and after the 3 July and 28 August 2019 Paroxysmal Eruptions

“…The differences mentioned above could be the results of structural changes that occurred in the shallower portion of the central conduits after the 2007 eruption [32]. However, analyzing the magmatic and structural processes involved in the 2019 eruptions and leading to further interpretations is beyond the scope of this paper and the reader is referred to the recent literature for additional details [27,34,38,39,68,69].…”

“…This characteristic activity is accompanied by lava flows at intervals of a few weeks (lava overflows) to a few years and, occasionally, is interrupted by discrete, more violent explosive events. The violent explosions are classified as major explosions and paroxysms, or called small-scale and large-scale paroxysms, respectively [26][27][28]. Small-scale paroxysms usually eject decimeter-sized blocks and bombs in the upper part of the volcano for a few minutes, associated with moderate ash and lapilli fallout at greater distances, e.g., [26].…”

“…The activity maintained very high frequency and intensity levels until, a few days later, the first paroxysm (3 July 2019) deeply disrupted the crater terrace and part of the upper portion of the SdF (Figure 1). This event involved both the north (hereafter N) and the central-south (hereafter CS) crater areas [27,[34][35][36][37][38][39]. The paroxysmal eruption generated an eruptive plume rising 6-8 km above the island's summit (924 m a.s.l., Vancori peak) [34,38], while the incandescent pyroclasts set fire to vegetation on the flanks of the volcano, resulting in a fire-damaged area of 39% of the total area of the island [40] and about 70% of the vegetated areas.…”

“…On 28 August 2019, the second paroxysmal eruption occurred, again modifying the morphology of the summit area and producing an eruptive column estimated up to 6 km above the summit [27,38,39,[43][44][45]. Pyroclasts from the eruption and debris from the collapsed rim of the CS area contributed to the generation of a pyroclastic current that again travelled down the SdF and out to sea.…”

Open-vent volcanoes: a preface to the special issue

“…However, open-vent volcanoes remain puzzling in various aspects and forecasting their behaviour is still challenging. Some of these volcanoes have a clear bimodal eruptive pattern with well-established surface activity, interrupted at times by paroxysms, as has been noted for Stromboli (Italy; Bertagnini et al 2011;Rose et al 2013;Métrich et al 2021) and Villarica (Chile; Johnson and Palma 2015;Aiuppa et al 2017). Such paroxysmal eruptions and hazardous fissure-type eruptions that can drain persistent lava lakes resident in summit craters, as at Ambrym for example (Németh and Cronin 2011;Shreve et al 2019), represent one of the major hazards at open-vent volcanoes.…”