Comment on egusphere-2025-6430

Le résumé fourni par la source

Abstract. Water vapor (H2O) dominates volcanic gas emissions globally with > 70 mol% of total volatile discharge, yet accurate H2O flux measurements remain challenging due to high atmospheric background and H2O’s spectroscopic and physical complexities. We developed a multi-band near-infrared (NIR) camera system, calibrated with an in-situ Multi-GAS instrument to quantify volcanic H2O flux. By combining plume speed measurement with H2O absorption data, we derived the H2O fluxes under favorable atmospheric conditions. We tested our approach at two contrasting volcanic settings: the passively degassing, high altitude, arid atmosphere Lascar volcano (Chile), and at the actively erupting, sea-level, humid atmosphere Fagradalsfjall volcano (Iceland) during the Litli Hrútur 2023 eruption. In November 26–29, 2022, and December 29, 2024, Lascar emitted 23,115 ± 10,694 t d-1 and 46,891 ± 18,863 t d-1 of H2O, respectively, higher than previous estimates using traditional SO2-based methods. In July/August 2023, the Litli Hrútur eruption averaged 19,108 ± 7,560 t d-1 of H2O emissions, matching petrological estimates and steadily declining towards the end of the eruption. The simultaneous deployment of NIR camera, miniDOAS, and a UV camera prove that H2O and SO2 emissions vary independently, with Multi-GAS H2O/SO2 ratios fluctuating over time. This variability challenges traditional measurements and demonstrates that independent direct measurements of major gases (H2O, CO2, and SO2) are essential for accurate volatile budgets and understanding volcanic degassing processes. Our work shows that the NIR camera approach provides a high-rate near-real time and direct method to obtain and visualize H2O emission rates.

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