Aiuppa, Alessandro

volatiles’ abundance and origin in their mantle sources. Here, we add new piece of knowledge to our understanding of volatile geochemistry in global OIB magmas, by presenting new noble gas (He-Ne-Ar) and carbon (C) isotope results for olivine- and clinopyroxene-hosted FI from enclaves, lavas, tephra and volcanic gas samples from Fogo, the only frequently active volcano at the Cape Verde archipelago (eastern Atlantic Ocean). FI, together with crater fumaroles, constrain the Fogo 3He/4He signature at 7.14–8.44 Rc/Ra (where RC is the aircorrected 3He/4He isotope ratio, and Ra is the same ratio in air), which is within the typical MORB (Mid- Ocean Ridge Basalt) mantle. The carbon isotopic ratio (δ13C vs. Pee Dee Belemnite) of CO2 in FI and fumaroles range from -6.04 to -4.41 ‰. We identify systematic variations of δ13C and He/Ar* with FI entrapment pressure (estimated from a combination of host mineral barometry and FI microthermometry), from which we develop a model for volatile degassing in the mantle-to-crustal magma storage system. The model predicts a crustal-like signature for carbon (δ13C of -0.4 ± 1.0 ‰) in primary melts formed by mantle melting at ~2200 MPa (~77 km) and a source He/Ar* ratio of 0.90–0.24, which are indicative of variably depleted mantle metasomatized by carbon enriched melts/fluids from a crustal component. We also use our results to characterise regional (in the Cape Verde and Canary archipelagos) and global trends in C and He isotope composition from OIB. From a comparison with the few other OIB localities for which δ13C are available, we propose that a carbon enriched crustal component could be recurrent at a global scale in OIB magmatism, although often masked by isotope fractionation during magmatic degassing. We additionally find that, at regional scale, He isotopes in OIB scale inversely correlate with the degree of partial melting of the mantle beneath individual islands’ (inferred from the La/Yb ratio of erupted basalts). More widely, our results corroborate previously established global relationships between OIB He isotopic signature, plume buoyancy flux and overlying plate velocity. In this interpretation, the MORB-like 3He/4He (8 ± 1 Ra) at Fogo reflects a combination of (i) low to medium magma productivity, (ii)

Open conduit volcanoes erupt with the highest frequency on Earth. Their activity is characterized by an outgassing flux that largely exceeds the gas that could be released by the erupted magma; and by frequent small explosions intercalated by larger events that pose a significant risk to locals, tourists, and scientists. Thus, identifying the signs of an impending larger explosion is of utmost importance for the mitigation of volcanic hazard. Larger explosive events have been associated with the sudden ascent of volatile rich magmas, however, where and why magma accumulates within the plumbing system remains unclear. Here we show that the interaction between CO2-rich fluids and magma spontaneously leads to the accumulation of volatile-rich, low density and gravitationally unstable magma at depth, without the requirement of permeability barriers. CO2-flushing forces the exsolution of water and the increase of magma viscosity, which proceeds from the bottom of the magma column upward. This rheological configuration unavoidably leads to the progressive thickening of a gas-rich and low density (i.e., gravitationally unstable) layer at the bottom of the feeding system. Our calculations account for observations, gas monitoring and petrological data; moreover, they provide a basis to trace the approach to deeply triggered large or paroxysmal eruptions and estimate their size from monitoring data. Our model is finally applied to Stromboli volcano, an emblematic example of open conduit volcano, but can be applied to any other open conduit volcano globally and offers a framework to anticipate the occurrence of unexpectedly large eruptions.

This study combines volcanic gas compositions, SO2 flux and satellite thermal data collected at Nevado del Ruiz between 2018 and 2021. We find the Nevado del Ruiz plume to have exhibited relatively steady, high CO2 compositions (avg. CO2/ST ratios of 5.4 ± 1.9) throughout. Our degassing models support that the CO2/ST ratio variability derives from volatile exsolution from andesitic magma stored in the 1-4 km depth range. Separate ascent of CO2-rich gas bubbles through shallow (< 1 km depth), viscous, conduit resident magma causes the observed excess degassing. We infer that degassing of ~ 974 mm3 of shallow (1-4 km) stored magma has sourced the elevated SO2 degassing recorded during 2018-2021 (average flux ~ 1548 t/d). Of this, only < 1 mm3 of magma have been erupted through dome extrusion, highlighting a large imbalance between erupted and degassed magma. Escalating deep CO2 gas flushing, combined with the disruption of passive degassing, through sudden accumulation and pressurization of bubbles due to lithostatic pressure, may accelerate volcanic unrest and eventually lead to a major eruption.

Some of the most CO2-rich magmas on Earth are erupted by intraplate ocean island volcanoes. Here, we characterise olivine-hosted melt inclusions from recent (<10 ky) basanitic tephra erupted by Fogo, the only active volcano of the Cape Verde Archipelago in the eastern Atlantic Ocean. We determine H2O, S, Cl, F in glassy melt inclusions and recalculate the total (glass + shrinkage bubbles) CO2 budget by three independent methodologies. We find that the Fogo parental basanite, entrapped as melt inclusion in forsterite-rich (Fo80-85) olivines, contains up to ~2.1 wt% CO2, 3–47 % of which is partitioned in the shrinkage bubbles. This CO2 content is among the highest ever measured in melt inclusions in OIBs. In combination with ~2 wt% H2O content, our data constrain an entrapment pressure range for the most CO2-rich melt inclusion of 648–1430 MPa, with a most conservative estimate at 773–1020 MPa. Our results therefore suggest the parental Fogo melt is stored in the lithospheric mantle at minimum depths of ~27 to ~36 km, and then injected into a vertically stacked magma ponding system. Overall, our results corroborate previous indications for a CO2-rich nature of alkaline ocean island volcanism. We propose that the Fogo basanitic melt forms by low degrees of melting (F = 0.06–0.07) of a carbonenriched mantle source, containing up to 355–414 ppm C. If global OIB melts are dominantly as carbon-rich as our Fogo results suggest, then OIB volcanism may cumulatively outgas

The persistent open-vent degassing of Mt. Etna is often punctuated by monthslong paroxysmal sequences characterized by episodes of violent Strombolian to lava fountaining activity. Understanding these gas-fueled transitions from quiescence to eruption requires routine measurement of gas fluxes. Here, we report SO2 flux measurements, obtained from a permanent UV camera system, collected over a two-year-long period spanning two paroxysmal sequences of Etna’s New South East Crater (NSEC) in December 2020/April 2021 and May/ October 2021. In both cases, SO2 flux increased from ≤ 3250 Mg/day during “ordinary” activity to ≥ 4200 Mg/day. We interpret these distinct SO2 degassing regimes in light of seismic and thermal observations and drawing on numerical simulations of sulfur degassing constrained by parental melt sulfur contents in Etna’s hawaiites. We find that initiation of a paroxysmal sequence results from an approximate doubling of the time-averaged rate of magma supply (and degassing) above the sulfur exsolution level (~150 MPa pressure), to >4m3/s. This corroborates recent models that argue for the triggering of paroxysmal sequences by escalating supply of volatile-rich magma to a reservoir ~3–4 km below the summit region. The non-stationary nature of magma flow and volcanic degassing we identify highlights the need for sustained surveillance to characterize long-term atmospheric budgets of volcanic volatiles

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 start- ing ~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.

We present a scenario-based, probabilistic hazard assessment for the San Salvador volcanic complex (SSVC), a volcanic field located in the vicinity of San Salvador that includes the El Boquer´on stratovolcano and 25 monogenetic vents. We define a set of likely eruption scenarios for tephra fallout and pyroclastic density currents (PDCs). The eruption scenarios range from violent Strombolian eruptions with a significant uncertainty in source position to sub-Plinian and Plinian activity fed from the central cone. The adopted methodology is mainly based on numerical modeling using Tephra2 (adopting the software TephraProb) to study tephra fallout and the branching box model and the branching energy cone model (adopting the programs BoxMapProb 2.0 and ECMapProb 2.0) to describe inertial and frictional PDCs, respectively. Despite the dominant W-WSW-trending winds, numerical results show that Plinian eruptions at El Boquer´on volcano are able to deposit thick tephra layers in the metropolitan area of San Salvador city, likely reaching mass loads of the order of 100 kg/m2 (conditional probability of 50%). The simulated sub-Plinian events highlight the seasonal influence of wind patterns. In fact, the conditional probability of significant tephra sedimentation in San Salvador city is strongly reduced when eruptions occur during the rainy season. Numerical modeling of violent Strombolian eruptions is performed considering uncertainty in vent position. Results show that the conditional probability of depositing tephra mass loads higher than 10 kg/m2 at a given point reaches a maximum value of ~7% on the NW flank of the volcano, at about 8 km from the central crater. On the other hand, very low conditional probabilities (<1%) are obtained for San Salvador city for any relevant threshold (10 kg/m2 or more) of tephra mass load during violent Strombolian events. Regarding PDCs, results show that those produced during large-scale Plinian eruptions are able to invade significant areas of the volcano surroundings, including San Salvador city. PDCs generated from the partial collapse of a sub-Plinian eruption column exhibit maximum inundation probabilities on the N, W and S flanks of the volcano. Cerro El Picacho exerts a significant shield effect on the propagation of these PDCs, with low inundation probabilities for San Salvador city (<3%). Finally, coupling published vent opening probability maps and numerical modeling of small-scale PDCs yields maximum inundation probabilities on the NW flank of the volcano, reaching maximum conditional probabilities of the order of ~10% and values of about 5% near the village of Nuevo Sitio del Nino.

The architecture of the magma storage system underneath Fogo Volcano (Cape Verde Archipelago) is characterised using novel fluid inclusion results from fifteen basanites, spanning the last 120 thousand years of volcanic activity, and encompassing a major flank collapse event at ~73 ka. Fluid inclusions, hosted in olivine and clinopyroxene, are made of pure CO2, and based on their textural characteristics, are distinguished in early (Type I) and late (Type II) stage. Inclusions homogenize to a liquid phase in the 2.8 to 30.8 ◦C temperature range. Densities values, recalculated assuming an original 10% H2O content at the time of trapping, range from 543 to 952 kg⋅m3, and correspond to entrapment or re-equilibration pressure ranges of 500–595 MPa, 700–740 MPa, and 245–610 MPa respectively for pre-collapse, early post-collapse, and Holocene/historical eruptions. These entrapment pressures are interpreted as reflecting the existence of two main magma accumulation zones at ~25 km and ~ 13–21 km depth, and a zone of fluid inclusion re-equilibration at 9–12 km depth. There is evidence of a complex temporal evolution of the magma system. Historical eruptions, and especially the three most recent ones (occurred in 1951, 1995 and 2014–25), bring fluid inclusion evidence for transient, pre-eruptive shallow (9–17 km depth) magma ponding. Early post-collapse (60 ka) volcanics, in contrast, document fast magma transport from ~25 km, and suggest a reconfiguration of the magma system after the Monte Amarelo collapse event.

Alkaline mafic magmas forming intra-plate oceanic islands are believed to be strongly enriched in CO2 due to low-degree partial melting of enriched mantle sources. However, until now, such CO2 enhancement has not been verified by measuring CO2 degassing during a subaerial eruption. Here, we provide evidence of highly CO2-rich gas emissions during the 86-day 2021 Tajogaite eruption of Cumbre Vieja volcano on La Palma Island, in the Canary archipelago. Our results reveal sustained high plume CO2/SO2 ratios, which, when combined with SO2 fluxes, melt inclusion volatile contents and magma production rates at explosive and effusive vents, imply a magmatic CO2 content of 4.5 ± 1.5 wt%. The amount of CO2 released during the 2021 eruptive activity was 28 ± 14 Mt CO2. Extrapolating to the volume of alkaline mafic magmas forming La Palma alone (estimated as 4000 km3 erupted over 11 Ma), we infer a maximum CO2 emission into the ocean and atmosphere of 1016 moles of CO2, equivalent to 20% of the eruptive CO2 emissions from a large igneous province eruption, suggesting that the formation of the Canary volcanic archipelago produced a CO2 emission of similar magnitude as a large igneous province.

Bagana is a remote, highly active volcano, located on Bougainville Island in southeastern Papua New Guinea. The volcano has exhibited sustained and prodigious sulfur dioxide gas emissions in recent decades, accompanied by frequent episodes of lava extrusion. The remote location of Bagana and its persistent activity have made it a valuable case study for satellite observations of active volcanism. This remoteness has also left many features of Bagana relatively unexplored. Here, we present the first measurements of volcanic gas composition, achieved by unoccupied aerial system (UAS) flights through the volcano's summit plume, and a payload comprising a miniaturized MultiGAS. We combine our measurements of the molar CO2/SO2 ratio in the plume with coincident remote sensing measurements (ground- and satellite-based) of SO2 emission rate to compute the first estimate of CO2 flux at Bagana. We report low SO2 and CO2 fluxes at Bagana from our fieldwork in September 2019, ∼320 ± 76 td −1 and ∼320 ± 84 td −1, respectively, which we attribute to the volcano's low level of activity at the time of our visit. We use satellite observations to demonstrate that Bagana's activity and emissions behavior are highly variable and advance the argument that such variability is likely an inherent feature of many volcanoes worldwide and yet is inadequately captured by our extant volcanic gas inventories, which are often biased to sporadic measurements. We argue that there is great value in the use of UAS combined with MultiGAS-type instruments for remote monitoring of gas emissions from other inaccessible volcanoes.