[S-TT34] Airborne surveys and monitoring of the Earth

[STT34-04] Development of an automatic volcanic plume sampler SelPS for UAS

★Invited Papers

*Urumu Tsunogai¹, Yutaka Miyagi¹, Ito Masanori¹, Fumiko Nakagawa¹, Shin Yoshikawa², Mitsuru Utsugi², Akihiko Yokoo² (1.Graduate School of Environmental Studies, Nagoya University, 2.Graduate School of Science, Kyoto University)

Keywords:fumarolic gases, volcanic plume, Carbon dioxide, Unoccupied Aerial Systems , automatic volcanic plume sampler

Both chemical and isotopic compositions of concentrated volcanic plumes are highly useful in evaluating the present status of active volcanoes. Monitoring their temporal changes is useful for forecasting volcanic eruptions as well. Recently, we developed a drone-borne automatic volcanic plume sampler, called SelPS, wherein an output signal from a sulfur dioxide (SO₂) sensor triggered a pump to collect plume samples when the SO₂ concentration exceeded a predefined threshold (Shingubara et al., JVGR, 2021). In addition, we added a radio transmission function to the sampler, which enabled our operator to monitor real-time SO₂ concentration during flights and thus obtain more concentrated volcanic plume samples through precise adjustment of the hovering position. We attached the improved SelPS to a drone at Nakadake crater, Aso volcano (Japan), and successfully obtained concentrated volcanic plume samples ejected from the crater (Tsunogai et al., Front. Earth Sci. 2022). Additionally, we found a significant linear correlation between the reciprocal of the concentration and isotopic ratios for the ²H/¹H ratios of H₂, ¹⁸O/¹⁶O ratios of CO₂, and ¹³C/¹²C ratios of CO₂ within the plume samples. Based on the isotopic ratios of fumarolic H2 (δ²H = −239 ± 6‰) and fumarolic CO₂ (δ¹³C = −3.58 ± 0.85‰ and δ18O = +22.01 ± 0.68‰) determined from the linear correlations, we estimated the apparent equilibrium temperatures (AETs) with magmatic H₂O simultaneously and precisely for the first time in erupting volcanoes, assuming hydrogen isotope exchange equilibrium between H₂ and H₂O (AET_D = 629 ± 32°C) and oxygen isotope exchange equilibrium between CO₂ and H₂O (AET_18O = 266 ± 65°C). We found that the AET_18O was significantly lower than the AET_D in the crater. While the temperature of the magmatic gases was originally 600°C or more, most of the gases cooled just beneath the crater to temperatures around the boiling point of water. The improved SelPS enable us to determine both AETD and AET18O in eruptive volcanoes, wherein fumaroles are inaccessible. Simultaneous and precise determination of both the AET18O and AETD can provide novel information on each volcano, such as the physicochemical conditions of magma degassing and the development of fluid circulation system.
This study was supported by MEXT Integrated Program for Next Generation Volcano Research and Human Resource Development (Theme B).