Search

Injecting volcanic gas into the air leads to an increase in carbon dioxide (CO2) levels compared with background concentrations and may establish gas hazard conditions. This study reports the results of five stable isotope (i.e., δ13C‐CO2 and δ18O‐CO2) surveys of airborne CO2 on Vulcano from August 2020 to November 2021. To measure CO2 in the air, a mobile laboratory was equipped with a laser‐based spectrophotometer that can selectively detect different CO2 isotopologues. Volcanic CO2 has a different isotopic signature than atmospheric CO2 and both δ13C‐CO2 and δ18O‐CO2 can help trace the injections of volcanic gases into the air. An isotopic mass balance model was developed for partitions CO2 between atmospheric background and volcanic CO2. The results of these studies show that volcanic CO2 emissions and atmospheric circulation deeply affected the concentration of CO2 in the air at Vulcano Porto. Studies of δ13C‐CO2 and δ18O‐CO2 provide an estimate of volcanic CO2 in the air. These results help identify spatially some points of interest for mitigating volcanic gas emission‐related hazards on Vulcano. Plain Language Summary: In volcanic areas, the concentration of CO2 in the air increases due to the dispersion of volcanic gases, as CO2 dominates among the local gas source components. Identifying variations in gas hazard due to changes in volcanic degassing is difficult when estimates of volcanic gases in air are based only on measurements of CO2 concentration. In this study, the effects of volcanic degassing on airborne CO2 are thoroughly evaluated by analyzing the isotopic composition of airborne CO2 during five onsite measurement surveys between August 2020 and November 2021. To quantify the contribution of volcanic CO2 to total CO2 in air, we developed a model based on the collected data using mass balance calculations. In 2021, a massive increase in volcanic degassing caused a clear increase of airborne CO2 concentration at Vulcano. We find that the effects of volcanic degassing depend on air turbulence, which changes throughout the day. The spatial variations in CO2 allow us to track the dispersion of volcanic gases in the air and their effects on gas hazards and atmospheric composition with unprecedented accuracy. Key Points: Spatial isotope monitoring enables the identification of the origin of CO2 in the airCalculating the stable isotope mass balances enables quantifying the volcanic CO2 in the total CO2 in the airSignificant changes in volcanic degassing increased air CO2 concentration and gas hazard on Vulcano—Italy—in 2021 [ABSTRACT FROM AUTHOR]

The La Fossa volcano on the Island of Vulcano, Italy, showed signs of more energetic fumarolic–solfataric activity during 2021. Several increases in volcanic gas emissions and seismicity, namely, "crisis," punctuated the passive degassing at Vulcano that had ensued after the last 1888–1890 vulcanian eruption. Most of the gases (i.e., up to 90%) were emitted at the crater cone while the diffuse degassing of CO2 at Vulcano Porto accounted for more than 10% of the volcanic emissions. Two anomalous degassing zones at the base of the volcanic cone (i.e., Palizzi and Faraglione) showed notable changes in the gas output during the volcanic crisis. In these zones, increases of soil CO2 flux (φCO2) had several practical implications other than of volcanological interest, owing to the risk related to people's exposure to volcanic gas emissions. The results of this study reveal variations of the average φCO2 from 74 g m−2 d−1 during September 2021 to 370 g m−2 d−1 in November 2021, which were 27% and 538% higher than the statistical background since 1988 (φCO2 ≈ 58 g m−2 d−1), respectively. These observations helped in volcanic surveillance at Vulcano. The soil CO2 partitioning determined using both φCO2 and carbon isotope measurements, helped track changes in the volcanic CO2 output from 9.97 · 104 to 101.15 · 104 kg d−1. Estimates for volcanic CO2 suggest that the instability of a magmatic body caused a transition from background fumarolic–solfataric activity toward an unrest event after September 2021. Plain Language Summary: A noticeable increase in volcanic outgassing occurred at Vulcano, Italy, in 2021. Although the volcano has not achieved critical conditions to produce an eruption, the soil CO2 emissions have prevented access into some zones of the island, due to the volcanic risk known as the gas hazard. Specialized instruments such as fluxmeters and spectrophotometers were used to measure the soil CO2 flux and the carbon isotopes of CO2 during four soil gas surveys. To understand why the volcanic system evolved toward a period of unrest, we modeled our measurements using mass balance calculations. We find that the CO2 increase, almost 10 times its baseline, was most likely due to the instability of a magmatic body within the mantle to crustal boundary known as the Moho discontinuity. Because of this magmatic instability, the volcanic CO2 emissions resumed in some zones of the island where volcanic activity had been dormant for decades. The resumption of volcanic degassing in a short period had not been recorded before at Vulcano, and it is important to understand its cause because future changes in magmatic activity might produce larger CO2 emissions that will have the added risk of gas hazards as well as that of an explosion. Key Points: Diffuse degassing surveys help track transition toward volcanic unrest periodsCarbon isotope composition allows quantification of the volcanic CO2 emitted by soilsSignificant changes in volcanic outgassing state caused increases in soil CO2 emissions and gas hazard at Vulcano—Italy—during 2021 [ABSTRACT FROM AUTHOR]

Abstract: Volcanic CO2 degassing is considered the primary process that controls the global carbon cycle over geological timescales. However, fluxes of CO2 from individual volcanoes, in particular those in past activities, have been poorly constrained. One way to estimate the flux is by using the H2OCO2 systematics of melt inclusions, which, according to petrological studies, records fluxing of a deep-derived CO2-rich fluid in the deep to shallow-level crustal magmatic systems. Assuming that this fluid fluxing is the process of volcanic CO2 emission, we quantified the fluxes of CO2 by combining a fluid transport model with melt inclusion data. We formulated CO2 fluxing as an advective fluid flow in a basaltic magma column with exchanging volatiles, and applied it to the melt inclusion data from Mount Etna, the type locality of a CO2-emitting volcano. The flux of CO2 was calculated to be 2.4–6.0kt/day, which is consistent with the observed volcanic CO2 emission rate of 1–10kt/day. We propose that this method potentially provides a means to quantify CO2 emission rates in past volcanic activities. Because CO2 fluxing is an open-system process, the estimated CO2 emission over geological timescales evaluated with this method should give much higher values than evaluations based simply on the volume of the erupted magmas. [Copyright &y& Elsevier]

Abstract: A better understanding of degassing processes at open-vent basaltic volcanoes requires collection of new datasets of H2O–CO2–SO2 volcanic gas plume compositions, which acquisition has long been hampered by technical limitations. Here, we use the MultiGAS technique to provide the best-documented record of gas plume discharges from Stromboli volcano to date. We show that Stromboli''s gases are dominated by H2O (48–98mol%; mean, 80%), and by CO2 (2–50mol%; mean, 17%) and SO2 (0.2–14mol%; mean, 3%). The significant temporal variability in our dataset reflects the dynamic nature of degassing process during Strombolian activity; which we explore by interpreting our gas measurements in tandem with the melt inclusion record of pre-eruptive dissolved volatile abundances, and with the results of an equilibrium saturation model. Comparison between natural (volcanic gas and melt inclusion) and modelled compositions is used to propose a degassing mechanism for Stromboli volcano, which suggests surface gas discharges are mixtures of CO2-rich gas bubbles supplied from the deep (>4km) plumbing system, and gases released from degassing of dissolved volatiles in the magma filling the upper conduits. The proposed mixing mechanism offers a viable and general model to account for composition of gas discharges at all volcanoes for which petrologic evidence of CO2 fluxing exists. A combined volcanic gas-melt inclusion-modelling approach, as used in this paper, provides key constraints on degassing processes, and should thus be pursued further. [Copyright &y& Elsevier]

Abstract: We investigated the dynamics of explosive activity at Mt. Etna between 31 August and 15 December 2006 by combining vesicle studies in the erupted products with measurements of the gas composition at the active, summit crater. The analysed scoria clasts present large, connected vesicles with complex shapes and smaller, isolated, spherical vesicles, the content of which increases in scoriae from the most explosive events. Gas geochemistry reports CO2/SO2 and SO2/HCl ratios supporting a deep-derived gas phase for fire-fountain activity. By integrating results from scoria vesiculation and gas analysis we find that the highest energy episodes of Mt. Etna activity in 2006 were driven by a previously accumulated CO2-rich gas phase but we highlight the lesser role of syn-eruptive vesicle nucleation driven by water exsolution during ascent. We conclude that syn-eruptive vesiculation is a common process in Etnean magmas that may promote a deeper conduit magma fragmentation and increase ash formation. [Copyright &y& Elsevier]

There is an urgent need to better constrain the global rates of mercury degassing from natural sources, including active volcanoes. Hitherto, estimates of volcanic fluxes have been limited by the poorly determined speciation of Hg in volcanic emissions. Here, we present a systematic characterisation of mercury partitioning between gaseous (Hg(g)) and particulate (Hg(p)) forms in the volcanic plume of Mount Etna, the largest open-vent passively degassing volcano on Earth. We demonstrate that mercury transport is predominantly in the gas phase, with a mean Hg(p)/Hg(g) ratio of ∼0.01 by mass. We also present the first simultaneous measurement of divalent gaseous mercury () and total gaseous mercury (Hg(g)) in a volcanic plume, which suggests that is the prevalent form of mercury in this context. These data are supported by the results of model simulations, carried out with HSC thermodynamic software. Based on a mean “bulk plume” Hg/SO2 mass ratio of 8.7×10−6, and a contemporaneous volcanic SO2 flux of 0.8Mtyr−1, we estimate an Hg emission rate from Mt. Etna during passive degassing of 5.4tyr−1 (range, 1.1–10tyr−1). This corresponds to ∼0.6% of global volcanic Hg emissions, and about 5% of Hg released from industrial activities in the Mediterranean area. [Copyright &y& Elsevier]