First In-Situ Measurements of Plume Chemistry at Mount Garet Volcano, Island of Gaua (Vanuatu)

Abstract

Recent volcanic gas compilations have urged the need to expand in-situ plume measurements to poorly studied, remote volcanic regions. Despite being recognized as one of the main volcanic epicenters on the planet, the Vanuatu arc remains poorly characterized for its subaerial emissions and their chemical imprints. Here, we report on the first plume chemistry data for Mount Garet, on the island of Gaua, one of the few persistent volatile emitters along the Vanuatu arc. Data were collected with a multi-component gas analyzer system (multi-GAS) during a field campaign in December 2018. The average volcanic gas chemistry is characterized by mean molar CO2/SO2, H2O/SO2, H2S/SO2 and H2/SO2 ratios of 0.87, 47.2, 0.13 and 0.01, respectively. Molar proportions in the gas plume are estimated at 95.9 ± 11.6, 1.8 ± 0.5, 2.0 ± 0.01, 0.26 ± 0.02 and 0.06 ± 0.01, for H2O, CO2, SO2, H2S and H2. Using the satellite-based 10-year (2005–2015) averaged SO2 flux of ~434 t d−1 for Mt. Garet, we estimate a total volatile output of about 6482 t d−1 (CO2 ~259 t d−1; H2O ~5758 t d−1; H2S ~30 t d−1; H2 ~0.5 t d−1). This may be representative of a quiescent, yet persistent degassing period at Mt. Garet; whilst, as indicated by SO2 flux reports for the 2009–2010 unrest, emissions can be much higher during eruptive episodes. Our estimated emission rates and gas composition for Mount Garet provide insightful information on volcanic gas signatures in the northernmost part of the Vanuatu Arc Segment. The apparent CO2-poor signature of high-temperature plume degassing at Mount Garet raises questions on the nature of sediments being subducted in this region of the arc and the possible role of the slab as the source of subaerial CO2. In order to better address the dynamics of along-arc volatile recycling, more volcanic gas surveys are needed focusing on northern Vanuatu volcanoes.

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“…The most recent configuration of the Multi-GAS, including details on sensor's accuracy and repeatability, calibration ranges and gas standards, is described in ref. 100 ). Our Multi-GAS version, assembled at UniPa, uses a Campbell CR6 datalogger to log simultaneously at 1 Hz the signals outputted from all sensors.…”

“…The map shows the spatial heterogeneity of the fumarolic CO 2 /SO 2 ratio in the fumarolic field, and is obtained by post-processing the results of the 16-18 November 2021 Multi-GAS walking traverses using the methodology of ref. 100 . This processing routine allows resolving the spatial heterogeneity of the fumarolic field with high temporal/spatial resolution, and is thus complementary to the standard protocol used to derive the ratios listed in Supplementary Table 2 (in which all data acquired nearby any single fumarole are jointly analysed).…”

Excess degassing drives long-term volcanic unrest at Nevado del Ruiz

“…For details on calibration and sensor range see ref. 51 . Ambient pressure, temperature and relative humidity were also measured, which allowed calculation of in-plume H 2 O concentrations using the Arden Buck equation 52 (Supplementary Table 3).…”

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“…Each fumarolic vent was monitored for a few minutes, so that the entire field (LF‐UF) was covered in ∼80 min. Our Multi‐GAS device included a Gascard nondispersive infrared (NDIR) spectrometer from Edinburgh Sensors (for CO 2 ) and two specific electrochemical sensors (both from City Technology) for SO 2 and H 2 S (see Lages et al., 2020, for a description of the most recent Multi‐GAS configuration, and for details on sensor's accuracy and repeatability, calibration ranges and gas standards). The system also measured temperature (T) and relative humidity (Rh; with a KVM3/5 Galltec‐Mela sensor), which were converted into H 2 O concentrations using the Arden Buck equation (Tamburello, 2015).…”