Moretti, Roberto

Volcano observatories (VOs) around the world are required to maintain surveillance of their volcanoes and inform civil protection and aviation authorities about impending eruptions. They often work through consolidated procedures to respond to volcanic crises in a timely manner and provide a service to the community aimed at reducing the potential impact of an eruption. Within the International Airways Volcano Watch (IAVW) framework of the International Civil Aviation Organisation (ICAO), designated State Volcano Observatories (SVOs) are asked to operate a colour coded system designed to inform the aviation community about the status of a volcano and the expected threats associated. Despite the IAVW documentation defining the different colour-coded levels, operating the aviation colour code in a standardised way is not easy, as sometimes, different SVOs adopt different strategies on how, when, and why to change it. Following two European VOs and Volcanic Ash Advisory Centres (VAACs) workshops, the European VOs agreed to present an overview on how they operate the aviation colour code. The comparative analysis presented here reveals that not all VOs in Europe use this system as part of their operational response, mainly because of a lack of volcanic eruptions since the aviation colour code was officially established, or the absence of a formal designation as an SVO. We also note that the VOs that do regularly use aviation colour code operate it differently depending on the frequency and styles of eruptions, the historical eruptive activity, the nature of the unrest, the monitoring level, institutional norms, previous experiences, and on the agreement they may have with the local Air Transport Navigation providers. This study shows that even though the aviation colour code system was designed to provide a standard, its usage strongly depends on the institutional subjectivity in responding to volcano emergencies. Some common questions have been identified across the different (S)VOs that will need to be addressed by ICAO to have a more harmonised approach and usage of the aviation colour code

Fumarolic gas survey of dormant volcanoes in hydrothermal activity is crucial to detect compositional and mass flux changes in gas emissions that are potential precursors of violent phreatic or even magmatic eruptions. Here we report on new data for the chemical compositions (CO2, H2S, SO2) and fluxes of fumarolic gas emissions (97–104°C) from La Soufrière volcano in Guadeloupe (Lesser Antilles) obtained from both mobile MultiGas measurements and permanent MultiGas survey. This paper covers the period 2016–2020, encompassing a period of enhanced hydrothermal unrest including an abrupt seismic energy release (M 4.1) on April 27, 2018. Our dataset reveals fumarolic CO2/H2S and SO2/H2S gas trends correlated to the evolution of surface activity and to other geochemical and geophysical parameters. We demonstrate that, even under tropical conditions (high humidity and rainfall), MultiGas surveys of low-T fumarolic emissions permit to distinguish deeply sourced signals of volcanic unrest from secondary changes in degassing due to shallow forcing processes such as water-gas-rock interactions in the hydrothermal system and meteorological effects.

magmatic volatiles

The fallout of ballistic blocks and bombs ejected from eruptive vents has the potential to produce severe injuries to people and damage to infrastructure in areas proximal to volcanoes. The dimensions and dispersions of ballistic ejecta from explosive eruptions are pivotal parameters to forecast the potential impact associated with future eruptions based on the compilation of probabilistic hazard maps. In this study, we propose a new probabilistic hazard quantification strategy to provide the probability of Volcanic Ballistic Projectiles (VBPs) to exceed some critical kinetic energy thresholds, considering a variability on the site of the eruptive vents and the effect of wind. La Soufrière de Guadeloupe (Lesser Antilles) is chosen as a test case, focussing on the most likely style explosive scenario associated with the eruption of an active lava dome (including phreatic, Vulcanian and Strombolian eruptions). Sensitivity analyses have guided the optimization of input parameters to balance the results stability and computational costs, showing that the topography is a pivotal factor when accounting for the spatial uncertainty on vent locations in the proximity of the dome area. Given an eruption within the adopted scenario, we provide maps showing the probability to exceed different energy reference thresholds for roof's perforation if at least one VBP falls in a target area. These maps are then combined with exposed elements to produce a qualitative exposure-based risk map. We compute the overall probability, conditional on the selected scenario, for roof perforation in a given area when a VBP is ejected. Results show probabilities varying from ca. 2% up to 40% within a few km from the volcano, quickly dropping away from the dome. However, when the probability to exceed the energy reference threshold is only conditional on falling of VBPs in a target area, most of Basse-Terre island would be affected by the 20–60% probability of roof perforation. This work confirms how the choice of a probabilistic approach is key to estimate the likelihood of occurrence of VBPs impacts as a first step towards the development and implementation of pro–active risk reduction strategies in volcanic areas.

The benign fuming activity of dormant volcanoes is punctuated by phases of escalating degassing activity that, on some occasions, ultimately prelude to eruption. However, understanding the drivers of such unrest is complicated by complex interplay between magmatic and hydrothermal processes. Some of the most comprehensively characterised degassing unrest have recently been observed at La Fossa cone on Vulcano Island, but whether or not these episodes involve new, volatile-rich ascending magma remains debated. Here, we use volcanic gas measurements, in combination with melt inclusion information, to propose that heightened sulphur dioxide flux during the intense fall 2021 La Fossa unrest is sourced by degassing of volatile-rich mafic magma. Calculations using a numerical model indicate observations are consistent with the unrest being triggered by the emplacement of ∼3·106 m3 of mafic magma at ∼4–5 km depth. Degassing of mafic magma is argued as a recurrent driver of unrest at dormant volcanoes worldwide.

Volcanic gas dispersal can be a serious threat to people living near active volcanoes since it can have short- and long-term effects on human health, and severely damage crops and agricultural land. In recent decades, reliable computational models have significantly advanced, and now they may represent a valuable tool to make quan- titative and testable predictions, supporting gas dispersal forecasting and hazard assessments for public safety. Before applying a specific modelling tool into hazard quantification, its calibration and its sensitivity to initial and boundary conditions should be carefully tested against available data, in order to produce unbiased hazard quantifications. In this study, we provided a number of prototypical tests aimed to validate the modelling of gas dispersal from a hazard perspective. The tests were carried out at La Soufrière de Guadeloupe volcano, one of the most active gas emitters in the Lesser Antilles. La Soufrière de Guadeloupe has shown quasi-permanent degassing of a low-temperature hydrothermal nature since its last magmatic eruption in 1530 CE, when the current dome was emplaced. We focused on the distribu- tion of CO2 and H2S discharged from the three main present-day fumarolic sources at the summit, using the mea- surements of continuous gas concentrations collected in the period March–April 2017. We developed a new probabilistic implementation of the Eulerian code DISGAS-2.0 for passive gas dispersion coupled with the mass-consistent Diagnostic Wind Model, using local wind measurements and atmospheric stability information from a local meteorological station and ERA5 reanalysis data. We found that model outputs were not significantly affected by the type of wind data but rather upon the relative positions of fumaroles and measurement stations. Our results reproduced the statistical variability in daily averages of observed data over the investigated period within acceptable ranges, indicating the potential usefulness of DISGAS-2.0 as a tool for reproducing the observed fumarolic degassing and for quantifying gas hazard at La Soufrière. The adopted testing procedure allows for an aware application of simulation tools for quantifying the hazard, and thus we think that this kind of testing should actually be the first logical step to be taken when applying a simulator to assess (gas) hazard in any other volcanic contexts.

After 25 years of gradual increase, volcanic unrest at La Soufrière of Guadeloupe reached its highest seismic en- ergy level on 27 April 2018, with the largest felt volcano-tectonic (VT) earthquake (ML 4.1 or MW 3.7) recorded since the 1976–1977 phreatic eruptive crisis. This event marked the onset ofa seismic swarm(180 events, 2 felt) occurring after three previous swarms on 3–6 January (70 events), 1 st February (30 events, 1 felt) and 16–17 April (140 events, 1 felt). Many events were hybrid VTs with long-period codas, located 2–4 km below the vol- cano summit and clustered within 2 km along a regional NW-SE fault cross-cutting La Soufrière. Elastic energy release increased with eachswarmwhereas inter-event time shortened. At the same time, summit fractures con- tinued to open and thermal anomalies to extend. Summit fumarolic activity increased significantly until 20 April, with a maximum temperature of111.4 °C and gas exit velocity of80 m/s, before declining to ~95 °C and ~33 m/s on 25 April. Gas compositions revealed increasing C/S and CO2/CH4 ratios and indicate hydrothermal P-T condi- tions that reached the critical point ofpure water. Repeated MultiGAS analysis of fumarolic plumes showed in- creased CO2/H2S ratios and SO2 contents associated with the reactivation of degassing fractures (T = 93 °C, H2S/SO2 ≈ 1). While no direct evidence ofupward magma migration was detected, we attribute the above phe- nomena to an increased supply ofdeepmagmatic fluids that heated and pressurized the La Soufrière hydrother- mal system, triggering seismogenic hydro-fracturing, and probable changes in deep hydraulic properties (permeability) and drainage pathways, which ultimately allowed the fumarolic fluxes to lower. Although this magmatic fluid injectionwasmodulated by the hydrothermal system, the unprecedented seismic energy release and the critical point conditions ofhydrothermal fluids suggest that the 2018 sequence ofevents can be regarded as a failed phreatic eruption. Should a similar sequence repeat, we warn that phreatic explosive activity could re- sult fromdisruption ofthe shallowhydrothermal system that is currently responsible for 3–9mm/y ofnearly ra- dial horizontal displacements within 1 km from the dome. Another potential hazard is partial collapse of the dome's SW flank, already affected by basal spreading above a detachment surface inherited from past collapses. Finally, the increased magmatic fluid supply evidenced by geochemical indicators in 2018 is compatible with magma replenishment of the 6–7 kmdeep crustal reservoir feeding La Soufrière and, therefore, with a potential evolution of the volcano's activity towards magmatic conditions.

Induced seismicity can be associated to the activity of fluid withdrawal and injection from/into the shallow crust (fracking, wastewater disposal into the deep crust, Enhanced Geothermal Systems technology, fluid extraction in oil fields and geothermal power plants). Long-term injection of large volumes of fluids is normally associated with induced seismicity, but the effect of withdrawal-reinjection in the same reservoir is less known, at least regarding its relation to simple injection. However, it is common experience worldwide that small (i.e. 10 MW or less) geothermal plants with withdrawal and re-injection of fluids in the same reservoir are mostly not associated with significant induced/triggered seismicity. This paper aims at understanding how to discriminate, on a numerical modelling basis, the seismogenic potential of withdrawal-reinjection with respect to injection only. With this aim, we analysed the induced pressure changes, the perturbed volumes of rocks and the potential for induced seismicity due to these operations. A set of simulations of injection or withdrawal-reinjection cycles, obtained by using the numerical code TOUGH2®, is applied to simple models of geothermal reservoirs, with varying permeability and lateral boundary constraints. For each permeability model, we then compare the time growth of perturbed volumes obtained with withdrawal-reinjection cycles to those obtained during simple injection, using the same flow rates. The size of perturbed volumes is then related to the maximum magnitude of induced/triggered seismicity, using models accredited in recent literature. Our results show that, for all models, withdrawal-reinjection is by far less critical than simple injection, because the perturbed volumes are remarkably smaller and remain constant over the simulated time, so minimizing the likelihood of interference with seismogenic faults. These results have significant implications for geothermal projects, and in the assessment of the potential risk related to fluid stimulation and induced seismicity.

Over the past two decades, La Soufrière volcano in Guadeloupe has displayed a growing degassing unrest whose actual source mechanism still remains unclear. Based on new measurements of the chemistry and mass flux of fumarolic gas emissions from the volcano, here we reveal spatio-temporal variations in the degassing features that closely relate to the 3D underground circulation of fumarolic fluids, as imaged by electrical resistivity tomography, and to geodetic-seismic signals recorded over the past two decades. Discrete monthly surveys of gas plumes from the various vents on La Soufrière lava dome, performed with portable MultiGAS analyzers, reveal important differences in the chemical proportions and fluxes of H2O, CO2, H2S, SO2 and H2, which depend on the vent location with respect to the underground circulation of fluids. In particular, the main central vents, though directly connected to the volcano conduit and preferentially surveyed in past decades, display much higher CO2/SO2 and H2S/SO2 ratios than peripheral gas emissions, reflecting greater SO2 scrubbing in the boiling hydrothermal water at 80–100 m depth. Gas fluxes demonstrate an increased bulk degassing of the volcano over the past 10 years, but also a recent spatial shift in fumarolic degassing intensity from the center of the lava dome towards its SE–NE sector and the Breislack fracture. Such a spatial shift is in agreement with both extensometric and seismic evidence of fault widening in this sector due to slow gravitational sliding of the southern dome sector. Our study thus provides an improved framework to monitor and interpret the evolution of gas emissions from La Soufrière in the future and to better forecast hazards from this dangerous andesitic volcano.

The Campi Flegrei caldera in Southern Italy is one of the most populated active volcanoes on Earth. It has an unprecedented record of historical unrest and eruption that dates back to 2.2 ka BP and provides key insights for understanding the dynamic evolution of large calderas. Since 1950, it has undergone four episodes of caldera-wide uplift and seismicity, which have raised the coastal town of Pozzuoli, near the centre of unrest, up to 4.5 m and triggered the repeated evacuation of some 40,000 people. After about 20 years of subsidence, following the uplift peak reached in 1984, the caldera started a new, low rate uplift episode, accompanied by low magnitude seismicity and marked geochemical changes in fumaroles. In this area it is crucial to discriminate episodes of shallow magma intrusion from hydrothermal perturbations, which are both able to generate unrest signals. In this paper, by a critical review of previous literature and some new results, we discriminate, in the unrest episodes, the relative contributions of hydrothermal effects and shallow magma intrusions. Our review is aimed also to show the different behavior of the largest unrest episodes, such as the 1982–1984, and the present, ungoing unrest characterized by smaller rate but longer lasting uplift. We show that for the former, larger uplift of the 80's, there is clear evidence for shallow magma intrusion, and we are able to compute the amount of intruded magma volume. For the present, on-going uplift, on the contrary, there is no evidence for magmatic activity at shallow depth. As a main result of our analysis, we demonstrate here the present unrest, characterized by much lower uplift rates and seismicity, is only interpretable as due to large gas fluxes coming from the deeper magma reservoir; without any appreciable contribution from shallow magma or recent magmatic intrusion. Our results shed new light on the interpretation of caldera unrest worldwide, and clearly indicate the most constraining data and the most rigorous procedures of data analysis for a correct interpretation of volcanic unrest