Here we introduce a Special Issue of Geosciences focused on the scientific research field of ‘Volcanic Plumes: Impacts on the atmosphere and insights into volcanic processes’ [...]
Direct sampling (filter pack and impactor) and remote sensing (ultraviolet spectroscopy and Sun photometry) of the plumes of Lascar and Villarrica volcanoes, Chile, reveal that both are significant and sustained emitters of SO 2 (28 and 3.7 kg s −1 , respectively), HCl (9.6 and 1.3 kg s −1 , respectively), HF (4.5 and 0.3 kg s −1 , respectively) and near‐source sulfate aerosol (0.5 and 0.1 kg s −1 , respectively). Aerosol plumes are characterized by particle number fluxes (0.08–4.0 μm radius) of ∼10 17 s −1 (Lascar) and ∼10 16 s −1 (Villarrica), the majority of which will act as cloud condensation nuclei at supersaturations >0.1%. Impactor studies suggest that the majority of these particles contain soluble SO 4 2− . Most aerosol size distributions were bimodal with maxima at radii of 0.1–0.2 μm and 0.7–1.5 μm. The mean particle effective radius ( R eff ) ranged from 0.1 to 1.5 μm, and particle size evolution during transport appears to be controlled by particle water uptake (Villarrica) or loss (Lascar) rather than sulfate production.
Abstract 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 CO 2 /SO 2 ratio in the plume with coincident remote sensing measurements (ground‐ and satellite‐based) of SO 2 emission rate to compute the first estimate of CO 2 flux at Bagana. We report low SO 2 and CO 2 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.
Existing studies of the composition of volcanic plumes generally interpret the presence of sulfate aerosol as the result of comparatively slow oxidation of gaseous SO 2 . We report here new observations from Masaya Volcano, Nicaragua, which demonstrate that sulfate aerosol may also be emitted directly from volcanic vents. Simultaneous aerosol and gaseous S, Cl, and F compounds were collected at the rim of the passively degassing crater in May 2001. Mean concentrations of SO 4 2− , Cl − , and F − within the plume were 83, 1.2, and 0.37 μg m −3 , respectively (fine aerosol fraction <2.5 μm) and 16, 2.5, and 0.56 μg m −3 , respectively (coarse aerosol fraction >2.5 μm). The aerosols were highly acidic, with estimated pH of <1.0 in the fine aerosols. Sulfate was present mainly in smaller particles, with the fine fraction accounting for ≈80% of the mass. The bulk of the sulfate was emitted directly from the magmatic vent. Acidity in the aerosols derived from the presence of sulfuric acid and, to a lesser extent, hydrofluoric acid, with [H + ]/[SO 4 2− ] equivalent values of 0.5–0.8 and 0.3–3 for fine and coarse aerosols, respectively. Gas phase/aerosol phase mass ratios were, on average, 458 (S), 330 (F), and 186 (Cl), with ranges of 95–1178, 37–659, and 43–259, respectively. These observations of highly acidic aerosol emitted directly from crater vents have implications for plume chemistry and environmental and health impacts of volcanic degassing.
One of the major problems in the volcanic surveillance is how data from several techniques can be correlated and used to discriminate between possible precursors of volcanic eruptions and changes related to non-eruptive processes. Gas chemical surveys and measurements of SO 2 emission rates performed in the past (2006–2019) at Lastarria volcano in Northern Chile have revealed a persistent increment of magmatic sourced gas emissions since late November 2012, following a 13 years period of intense ground uplift. In this work, we provide new insights into the gas-chemical evolution of Lastarria’s fumarolic discharges obtained from direct sampling (2006–2019) and SO 2 emission rates using UV camera and DOAS instruments (2018–2019) and link these to pre-existing information on ground deformation (1998–2016) in order to determine the origin of observed degassing and ground deformation processes. We revise the four mechanisms originally proposed as alternatives by Lopez et al. (Geosphere, 2018, 14 (3), 983–1007) to explain the changes observed in the fluid geochemistry and ground deformation between 2009 and 2012, in order to explain major changes in gas-geochemistry over an extended period between 1998 and 2019. We hypothesize that a continuous sequence of processes explains the evolution in the fluid geochemistry of fumarolic discharges. Two mechanisms are responsible of the changes in the gas composition during the studied period, corresponding to a 1) deep magma chamber (7–15 km depth) pressurized by volatile exsolution (1998–2020), which is responsible of the large-scale deformation; followed by 2) a crystallization-induced degassing (2001–2020) and pressurization of the hydrothermal system (2003-early November 2012), where the former process induced the changes in the gas composition from hydrothermal-dominated to magmatic-dominated, whereas the last produced the small-scale deformation at Lastarria volcano. The changes in the gas composition since late November 2012, which were strongly dominated by magmatic volatiles, produced two consecutive processes: 1) acidification (late November 2012–2020) and 2) depletion (2019–2020) of the hydrothermal system. In this work we have shown that a long-term surveillance of the chemistry of fluid discharges provides valuable insights into underlying magmatic/volcanic processes, and consequently, for forecasting future eruptions.
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