Tunable diode laser measurements of hydrothermal/volcanic CO2 and implications for the global CO2 budget

Quantifying the CO2 flux sustained by low-temperature fumarolic fields in hydrothermal/volcanic environments has remained a challenge, to date. Here, we explored the potential of a commercial infrared tunable laser unit for quantifying such fumarolic volcanic/hydrothermal CO2 fluxes. Our field tests were conducted between April 2013 and March 2014 at Nea Kameni (Santorini, Greece), Hekla and Krýsuvík (Iceland) and Vulcano (Aeolian Islands, Italy). At these sites, the tunable laser was used to measure the path-integrated CO2 mixing ratios along cross sections of the fumaroles' atmospheric plumes. By using a tomographic post-processing routine, we then obtained, for each manifestation, the contour maps of CO2 mixing ratios in the plumes and, from their integration, the CO2 fluxes. The calculated CO2 fluxes range from low (5.7 ± 0.9 t d−1; Krýsuvík) to moderate (524 ± 108 t d−1; La Fossa crater, Vulcano). Overall, we suggest that the cumulative CO2 contribution from weakly degassing volcanoes in the hydrothermal stage of activity may be significant at the global scale

Tunable diode laser measurements of hydrothermal/volcanic CO2 and implications for the global CO2 budget

Quantifying the CO2 flux sustained by lowtemperature fumarolic fields in hydrothermal/volcanic environments has remained a challenge, to date. Here, we explored the potential of a commercial infrared tunable laser unit for quantifying such fumarolic volcanic/hydrothermal CO2 fluxes. Our field tests were conducted between April 2013 and March 2014 at Nea Kameni (Santorini, Greece), Hekla and Krýsuvík (Iceland) and Vulcano (Aeolian Islands, Italy). At these sites, the tunable laser was used to measure the path-integrated CO2 mixing ratios along cross sections of the fumaroles’ atmospheric plumes. By using a tomographic post-processing routine, we then obtained, for each manifestation, the contour maps of CO2 mixing ratios in the plumes and, from their integration, the CO2 fluxes. The calculated CO2 fluxes range from low (5.7 +/- 0.9 t d-1; Krýsuvík) to moderate (524 +/-108 t d-1; La Fossa crater, Vulcano). Overall, we suggest that the cumulative CO2 contribution from weakly degassing volcanoes in the hydrothermal stage of activity may be significant at the global scale

Escalating CO2 degassing at the Pisciarelli fumarolic system, and implications for the ongoing Campi Flegrei unrest

This short communication aims at providing an updated report on degassing activity and ground deformation variations observed during the ongoing (2012–2019) Campi Flegrei caldera unrest, with a particular focus on Pisciarelli, currently its most active fumarolic field. We show that the CO2 flux from the main Pisciarelli fumarolic vent (referred as “Soffione”) has increased by a factor > 3 since 2012, reaching in 2018–2019 levels (>600 tons/day) that are comparable to those typical of a medium-sized erupting arc volcano. A substantial widening of the degassing vents and bubbling pools, and a further increase in CO2 concentrations in ambient air (up to 6000 ppm), have also been detected since mid-2018. We interpret this escalating CO2 degassing activity using a multidisciplinary dataset that includes thermodynamically estimated pressures for the source hydrothermal system, seismic and ground deformation data. From this analysis, we show that degassing, deformation and seismicity have all reached in 2018–2019 levels never observed since the onset of the unrest in 2005, with an overall uplift of ~57 cm and ~448 seismic events in the last year. The calculated pressure of the Campi Flegrei hydrothermal system has reached ~44 bar and is rapidly increasing. Our results raise concern on the possible evolution of the Campi Flegrei unrest and reinforce the need for careful monitoring of the degassing activity at Pisciarelli, hopefully with the deployment of additional permanent gas monitoring units

Tracking Formation of a Lava Lake From Ground and Space: Masaya Volcano (Nicaragua), 2014–2017

A vigorously degassing lava lake appeared inside the Santiago pit crater of Masaya volcano (Nicaragua) in December 2015, after years of degassing with no (or minor) incandescence. Here we present an unprecedented-long (3 years) and continuous volcanic gas record that instrumentally characterizes the (re)activation of the lava lake. Our results show that, before appearance of the lake, the volcanic gas plume composition became unusually CO2 rich, as testified by high CO2/SO2 ratios (mean: 12.2 ± 6.3) and low H2O/CO2 ratios (mean: 2.3 ± 1.3). The volcanic CO2 flux also peaked in November 2015 (mean: 81.3 ± 40.6 kg/s; maximum: 247 kg/s). Using results of magma degassing models and budgets, we interpret this elevated CO2 degassing as sourced by degassing of a volatile-rich fast-overturning (3.6–5.2 m3 s−1) magma, supplying CO2-rich gas bubbles from minimum equivalent depths of 0.36–1.4 km. We propose this elevated gas bubble supply destabilized the shallow (<1 km) Masaya magma reservoir, leading to upward migration of vesicular (buoyant) resident magma, and ultimately to (re)formation of the lava lake. At onset of lava lake activity on 11 December 2015 (constrained by satellite-based MODIS thermal observations), the gas emissions transitioned to more SO2-rich composition, and the SO2 flux increased by a factor ∼40% (11.4 ± 5.2 kg/s) relative to background degassing (8.0 kg/s), confirming faster than normal (4.4 versus ∼3 m3 s−1) shallow magma convection. Based on thermal energy records, we estimate that only ∼0.8 of the 4.4 m3 s−1 of magma actually reached the surface to manifest into a convecting lava lake, suggesting inefficient transport of magma in the near-surface plumbing system

Total (fumarolic 08+ 08diffuse soil) CO2 output from Furnas volcano

Furnas volcano, in Sao Miguel island (Azores), being the surface expression of rising hydrothermal steam, is the site of intense carbon dioxide (CO2) release by diffuse degassing and fumaroles. While the diffusive CO2 output has long (since the early 1990s) been characterized by soil CO2 surveys, no information is presently available on the fumarolic CO2 output. Here, we performed (in August 2014) a study in which soil CO2 degassing survey was combined for the first time with the measurement of the fumarolic CO2 flux. The results were achieved by using a GasFinder 2.0 tunable diode laser. Our measurements were performed in two degassing sites at Furnas volcano (Furnas Lake and Furnas Village), with the aim of quantifying the total (fumarolic + soil diffuse) CO2 output. We show that, within the main degassing (fumarolic) areas, the soil CO2 flux contribution (9.2 t day(-1)) represents a minor (similar to 15 %) fraction of the total CO2 output (59 t day(-1)), which is dominated by the fumaroles (similar to 50 t day(-1)). The same fumaroles contribute to similar to 0.25 t day(-1) of H2S, based on a fumarole CO2/H2S ratio of 150 to 353 (measured with a portable Multi-GAS). However, we also find that the soil CO2 contribution from a more distal wider degassing structure dominates the total Furnas volcano CO2 budget, which we evaluate (summing up the CO2 flux contributions for degassing soils, fumarolic emissions and springs) at similar to 1030 t day(-1)

Volcanic CO2 measurements at Campi Flegrei by Infrared Tunable Diode Laser absorption Spectroscopy

Gas studies add information for the interpretation of fluid circulation dynamics at dormant volcanoes and can contribute to eruption forecasting. Direct in-situ and remote-sensing techniques were used in order to improve volcanic gas monitoring, essential for hazard assessment. In the last decades, near-infrared diode lasers have increasingly been used in atmospheric research and, though in an experimental phase, are now finding applications in volcanic gas studies. The Tunable Diode Laser Spectroscopy technique (TDLS) relies on measuring the absorbance at specific wavelengths due to the absorption of IR radiation by a target gas. Here, we report on the application of the GasFinder 2.0, an infrared laser unit operating in the 1.3-1.7 μm wavelength range, to measuring CO2 mixing ratios in volcanic gas emissions. Three different campaigns were carried out at Campi Flegrei volcano (near Pozzuoli, Southern Italy) in the attempt to obtain novel information on the current degassing unrest of Solfatara and Pisciarelli fumarolic fields. At each site, we used the GasFinder unit and several retro-reflector mirrors, to scan the plumes from different angles and distances. From post-processing of the data, by using a tomographic Matlab routine, we resolved, for each of the manifestations, the contour maps of CO2 mixing ratios in their atmospheric plumes. From their integration (and after multiplication by the plumes’ transport speeds) we evaluated the CO2 fluxes. The so-calculated flux (about 490 Mg/day) supports a significant contribution of fumaroles to the global CO2 budget. The cumulative (fumaroles [this study] +soil [1]) CO2 output from Campi Flegrei is finally evaluated at 1600 Mg/day. The application of lasers to volcanic gas studies is still an emerging (though intriguing) research field, and requires more testing and validation experiments

• Volcanic CO2 measurements via Tunable Diode Laser Spectrometer

The analysis of volcanic gas datasets offer key information to build/validate geological models relevant to a variety of volcanic processes and behaviours, including eruptions. In the last decades, near-infrared room-temperature diode lasers, though in an experimental phase, are finding applications in volcanic gas studies. Here, we report on the application of the GasFinder 2.0, a commercial tunable diode infrared laser-receiver unit, operating in the 1.3-1.7 μm wavelength range, to measuring CO2 concentrations in volcanic gas emissions. At first, our field tests were conducted in three different campaigns at Campi Flegrei volcano (near Pozzuoli, Southern Italy), and, subsequently, also in other degassing systems (Nea Kameni volcano, Greece; Hekla Volcano and Krýsuvík hydrothermal area, Iceland). GasFinder repeatedly measured the path-integrated mixing ratios of CO2 along cross-sections of the atmospheric plumes of the main fumarolic fields in the investigated areas. At each site, we used an ad-hoc designed measurement geometry, using the GasFinder unit and several retro-reflector mirrors, to scan the plumes from different angles and distances. From post-processing of the data, by using a tomographic Matlab routine, we resolved, for each of the manifestations, the contour maps of CO2 mixing ratios in their atmospheric plumes. From their integration (and after multiplication by the plumes’ transport speeds), we evaluated the CO2 fluxes. The so-calculated fluxes ranged from ∼5.7 (Krýsuvík) to ∼490 (Campi Flegrei) tons/day, supporting a significant contribution of fumaroles to the global CO2 budget

Volcanic gas monitoring of quiescent volcanoes using permanent Multi-GAS networks

The Multi-component Gas Analyzer System (Multi-GAS) has recently consolidated as a standard technique for the nearly real-time in-situ observation of major volcanogenic components (H2O, CO2, SO2, H2S,H2) in volcanic gas plumes. The Multi-GAS has been initially operated at open-vent volcanoes, where it has revealed ideal for long-term continuous observations at for instance Etna and Stromboli volcanoes in Italy, therein paving the way to the acquisition of unprecedentedly long and continuous volcanic gas time-series. We here initially review the present state of the expanding network of permanent Multi-GAS instruments, now covering about 10 volcanoes worldwide. We then specifically focus on the results acquired via Multi-GAS monitoring of fumarolic activity at two quiescent, but potentially hazardous volcanoes in Europe: Santorini, in Greece, and Hekla, in Iceland. Our results overall demonstrate the potential of the Multi-GAS in the monitoring of even sluggish, weak fuming hydrothermal activity as currently observed at both Santorini and Hekla. Quantitative modeling of the results open the way to charactering magmatic-hydrothermal and gas-groundwater interactions with unprecedented detail. We show that, at both volcanoes, gas compositions range in time from H2O-rich (H2O/CO2 > 1) to CO2-dominated and S-poor (CO2/H2S > 10,000), a compositional trend which we quantitatively reproduce via model runs of gas-water-rock interactions initialized using EQ 3/6

Additional file 1: of Total (fumarolic + diffuse soil) CO2 output from Furnas volcano

The supplementary file is a more detailed documentation about the TDL acquisitions and data elaboration. A1. CO2 TDL-datasets. A2. Parameters used to perform sGs with CO2 concentrations TDL data and Zonal Statistic on E-Type maps. A3. Parameters used to perform sGs with soil CO2 flux data (accumulation chamber). In A1 section, each path laser-retroreflector acquisition during the campaigns carried out at Furnas Lake (Additional file 1: Table S1) and Furnas Village (Additional file 1: Table S2) is shown. In A2 section, more details about statistical approach and elaboration of data to create the distribution CO2 concentration maps are shown (Additional file 1: Tables S3, S4, and S5). Finally, parameters used to perform sGs with soil CO2 flux data are shown in A3 section (Tables S6 and S7)