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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., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Funder: IDEX-ISITE initiative16-IDEX-0001 (CAP 20-25), While a landslide at the volcanic island of Stromboli (Aeolian Islands, Italy) in December 2002 created a tsunami with a run-up of 10.9 m, two paroxysmal eruptions in the summer of 2019 caused a tsunami with an amplitude of 40 to 20 cm. All three events required rapid, spontaneous emergency evacuations of the beach zone as the time between tsunami generation and impact is around 4 min. These conditions thus require a special consideration of the issue of evacuation capabilities on the island in the event of a volcanogenic tsunami. The purpose of this paper is thus to (i) determine pedestrian evacuation times from high-risk coastal areas to safe zones, (ii) to assess building evacuation ease, and (iii) determine emergency evacuation plans (for buildings and coastal zones). For this purpose, we created a GIS-based risk analysis/mapping tool that also allowed macroscopic evacuation modelling. In our case, the high-risk zone to be evacuated involves an area extending to 10 m a.s.l. and involving 123 individual buildings over an area of 0.18 km2. The results show that 33% of the buildings can be evacuated in 4 min, and that a 10-min warning time is required for a complete and well-distributed evacuation whereby the population is evenly distributed between all evacuation exits to avoid the potential for congestion. Initial interviews of residents in the at-risk zone reveal a high level of awareness and a desire for personalized evacuation scenarios.

Recent gas flux measurements have shown that Strombolian explosions are often followed by periods of elevated flux, or “gas codas,” with durations of order a minute. Here we present UV camera data from 200 events recorded at Stromboli volcano to constrain the nature of these codas for the first time, providing estimates for combined explosion plus coda SO2 masses of ≈18–225 kg. Numerical simulations of gas slug ascent show that substantial proportions of the initial gas mass can be distributed into a train of “daughter bubbles” released from the base of the slug, which we suggest, generate the codas, on bursting at the surface. This process could also cause transitioning of slugs into cap bubbles, significantly reducing explosivity. This study is the first attempt to combine high temporal resolution gas flux data with numerical simulations of conduit gas flow to investigate volcanic degassing dynamics.

We describe a new volcanic hotspot detection system, named Middle InfraRed Observation of Volcanic Activity (MIROVA), based on the analysis of infrared data acquired by the Moderate Resolution Imaging Spectroradiometer sensor (MODIS). MIROVA uses the middle infrared radiation (MIR), measured by MODIS, in order to detect and measure the heat radiation deriving from volcanic activity. The algorithm combines spectral and spatial principles, allowing the detection of heat sources from 1 megawatt (MW) to more than 10 gigawatt (GW). This provides a unique opportunity to: (i) recognize small-scale variations in thermal output that may precede the onset of effusive activity; (ii) track the advance of large lava flows; (iii) estimate lava discharge rates; (iv) identify distinct effusive trends; and, lastly, (v) follow the cooling process of voluminous lava bodies for several months. Here we show the results obtained from data sets spanning 14 years recorded at the Stromboli and Mt Etna volcanoes, Italy, and we investigate the above aspects at these two persistently active volcanoes. Finally, we describe how the algorithm has been implemented within an operational near-real-time processing chain that enables the MIROVA system to provide data and infrared maps within 1–4 h of the satellite overpass.

Strombolian eruptions can be described in terms of growth, coalescence, and rise of a gas pocket (aka slug) bursting at the surface of a vent. This model overlooks that the transition to explosive regimes is mostly controlled by the permeability in the upper part of a volcanic conduit. We report here on the first gas flux measurements of Strombolian explosions from a vent that exhibited a significant decrease of passive degassing tens of second prior to the onset of the explosion. This particular explosive activity took place during the July 2014 lava overflows, when the magma level inside the conduit rose up to the crater terrace. The amount of gas that accumulated before the eruption is incredibly similar to the amount of gas ejected during the explosion. This similarity suggests a mechanism of decrease of the shallow conduit permeability and a subsequent accumulation of gas behind a cap of cold magma. The accumulated gas is then released when the over-pressure can open a leak on the cap of cold magma. Our unprecedented results offer key and novel insights into the explosive degassing dynamics within the shallow conduit systems of this open-vent volcano and probably at many other basaltic volcanoes.

Volcanic eruptions are often accompanied by release of huge amounts of magmatic SO2. Capturing sizeable precursory SO2 flux variations prior to eruption has revealed far more challenging, instead, in spite of the recent progresses in instrumental gas monitoring. Here, we report on the SO2 fluxes variations we detected at Stromboli volcano prior to the effusive eruption started on the 6th August 2014. The SO2 fluxes were regularly quantified at high-rate (0.5 Hz) using two fully autonomous permanent SO2 camera devices installed - within the framework the ERC-FP7 project "Bridge"- at two sites located at 0.5 km (Roccette) and 1.75 km (Sciara del Fuoco rim) distance from the crater terrace. This system provided sufficient spatial resolution, (~0.4 m) to allow for separate evaluation of gas emissions from the centrals/NE craters (CC and NEC, ~150 t/d on average) and from the northern hornitos (NH, ~15 t/d on average) that was active in summer 2014. Notwithstanding its marginal contribution to the total SO2 flux, the NH was vigorously active before the effusive eruption onset, and produced a large number of ash-free explosions, which individual SO2 output was easily measurable at high sampling rate with the SO2 cameras. From the beginning of June 2014, the NH exhibited a progressive increase of its explosive SO2 release (from ~1 t/d up to ~5 t/d) which culminated in correspondence with a sequence of lava overflows on the beginning of July 2014. A notable correlation between the explosive degassing pattern and co-acquired acoustic pressure and satellite-derived Volcanic Radiative Power was observed. The relative contributions of the individual degassing craters to the total gas emissions varied in response to the displacement of the magma level within the conduits, with the largest SO2 fluxes being observed during lava overflows. Our results here indicate detectable changes in the relative gas contribution from the different craters and in their degassing modes, although in the absence of sizeable pre-eruptive variations of the total SO2 output. Our observations offer new insights for the understanding of degassing dynamics within shallow conduit systems.