This paper examines phreatic eruptions which are driven by inputs of magma and magmatic gas. We synthesize data from several significant phreatic systems, including two in Costa Rica (Turrialba and Poas) which are currently highly active and hazardous. We define two endmember types of phreatic eruptions, the first (type 1) in which a deeper hydrothermal system fed by magmatic gases is sealed and produces overpressure sufficient to drive explosive eruptions, and the second (type 2) where magmatic gases are supplied via open-vent degassing to a near-surface hydrothermal system, vaporizing liquid water which drives the phreatic eruptions. The surficial source of type 2 eruptions is characteristic, while the source depth of type 1 eruptions is commonly greater. Hence, type 1 eruptions tend to be more energetic than type 2 eruptions. The first type of eruption we term “phreato-vulcanian”, and the second we term “phreato-surtseyan”. Some systems (e.g., Ruapehu, Poas) can produce both type 1 and type 2 eruptions, and all systems can undergo sealing at various timescales. We examine a number of precursory signals which appear to be important in understanding and forecasting phreatic eruptions; these include very long period events, banded tremor, and gas ratios, in particular H2S/SO2 and CO2/SO2. We propose that if these datasets are carefully integrated during a monitoring program, it may be possible to accurately forecast phreatic eruptions.

/pdf/understanding-and-forecasting-phreatic-eruptions-driven-by-o7947opri0.pdf

Understanding and forecasting phreatic eruptions driven by magmatic degassing

http://www.jlakes.org/config/hpkx/news_category/2015-05-10/1-s2.0-S037702731400002X.pdf

Past, present and future of volcanic lake monitoring

Abstract We review the state of knowledge on global volcanogenic Hg emissions to the atmosphere and present new data from seven active volcanoes (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely and Etna) and two geothermal fields (Las Pailas and Las Hornillas). The variability of Hg contents (c. 4–125 ng m−3) measured in gaseous emissions reflects the dynamic nature of volcanic plumes, where the abundances of volatiles are determined by the physical nature of degassing and variable air dilution. Based on our dataset and previous work, we propose that an average Hg/SO2 plume mass ratio of c. 7.8×10−6 (±1.5×10−6; 1 SE, n=13) is best representative of open-conduit quiescent degassing. Taking into account the uncertainty in global SO2 emissions, we infer a global volcanic Hg flux from persistent degassing of c. 76±30 t a−1. Our data are derived from active volcanoes during non-eruptive periods and we do not have any direct constraint on the Hg flux during periods of elevated SO2 flux associated with large-scale effusive or explosive eruptions. This suggests that the time-averaged Hg flux from these volcanoes is even larger if the eruptive contribution is considered. Conversely, closed-conduit degassing and geothermal emissions contribute modest amounts of Hg.

/pdf/mercury-fluxes-from-volcanic-and-geothermal-sources-an-4d1ykmvox6.pdf

Mercury fluxes from volcanic and geothermal sources: an update

Here we report on the first assessment of volatile fluxes from the hyperacid crater lake hosted within the summit crater of Copahue, a very active volcano on the Argentina-Chile border. Our observations were performed using a variety of in situ and remote sensing techniques during field campaigns in March 2013, when the crater hosted an active fumarole field, and in March 2014, when an acidic volcanic lake covered the fumarole field. In the latter campaign, we found that 566 to 1373 t d−1 of SO2 were being emitted from the lake in a plume that appeared largely invisible. This, combined with our derived bulk plume composition, was converted into flux of other volcanic species (H2O ~ 10989 t d−1, CO2 ~ 638 t d−1, HCl ~ 66 t d−1, H2 ~ 3.3 t d−1, and HBr ~ 0.05 t d−1). These levels of degassing, comparable to those seen at many open-vent degassing arc volcanoes, were surprisingly high for a volcano hosting a crater lake. Copahue's unusual degassing regime was also confirmed by the chemical composition of the plume that, although issuing from a hot (65°C) lake, preserves a close-to-magmatic signature. EQ3/6 models of gas-water-rock interaction in the lake were able to match observed compositions and demonstrated that magmatic gases emitted to the atmosphere were virtually unaffected by scrubbing of soluble (S and Cl) species. Finally, the derived large H2O flux (10,988 t d−1) suggested a mechanism in which magmatic gas stripping drove enhanced lake water evaporation, a process likely common to many degassing volcanic lakes worldwide.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015JB012160

Intense magmatic degassing through the lake of Copahue volcano, 2013-2014

Remote sampling of water from Yugama crater lake at Kusatsu-Shirane volcano, Japan, was performed using a drone. Despite the high altitude of over 2000 m above sea level, our simple method was successful in retrieving a 250 mL sample of lake water. The procedure presented here is easy for any researcher to follow who operates a drone without additional special apparatus. We compare the lake water sampled by drone with that sampled by hand at a site where regular samplings have previously been carried out. Chemical concentrations and stable isotope ratios are largely consistent between the two techniques. As the drone can fly automatically with the aid of navigation by Global Navigation Satellite System (GNSS), it is possible to repeatedly sample lake water from the same location, even when entry to Yugama crater lake is restricted due to the risk of eruption.

https://link.springer.com/content/pdf/10.1186/s40623-018-0835-3.pdf

Water sampling using a drone at Yugama crater lake, Kusatsu-Shirane volcano, Japan

Surface degassing is an important volatile discharge process for an active volcanic crater lake. The compositions of volcanic gases discharged from a lake surface (lake gas) were quantified by volcanic plume measurements using a Multi-GAS and alkaline-filter techniques at the Yudamari crater lake, Aso volcano, Japan. Compositions of the lake gases were quite variable and are clearly different from the gases from adjacent fumaroles. Differentiation processes of the lake gas, the lake water, and the fumarolic gases are evaluated based on their compositions. Concentrations of HCl in the lake gas and the lake water indicate that the lake gas composition is controlled by the equilibrium evaporation of the lake water at the lake temperature. Contrasting compositions of the lake gas and the lake water indicate that sulfate and elemental sulfur formation controls chemical differentiation in the lake. The composition of the hydrothermal fluids supplied to the lake is estimated based on mass balance of the lake gas and the lake water. The hydrothermal fluids have similar H2O/S and H2O/Cl ratios but lower CO2/S ratios than the fumarolic gases. This composition contrast indicates that the fumarolic gases are a mixture of magmatic gases and a vapor phase separated from the hydrothermal fluids supplied to the lake.

Degassing Activity of a Volcanic Crater Lake: Volcanic Plume Measurements at the Yudamari Crater Lake, Aso Volcano, Japan

Degassing of Aso Volcano, Japan through an Acid Crater Lake: Differentiation of Volcanic Gas-Hydrothermal Fluids Deduced from Volcanic Plume Chemistry

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Degassing Activity of a Volcanic Crater Lake: Volcanic Plume Measurements at the Yudamari Crater Lake, Aso Volcano, Japan

Degassing of Aso Volcano, Japan through an Acid Crater Lake: Differentiation of Volcanic Gas-Hydrothermal Fluids Deduced from Volcanic Plume Chemistry