[U-05] Natural Hydrogen, Understanding its Subsurface System and Production Engineering

[U05-P01] Enrichment of molecular hydrogen in the lower air of Mt. Apoi in the Horoman peridotite complex, Japan

*Urumu Tsunogai¹, Yutaka Miyagi¹, Wenhua RUAN¹, Yu Kitamura¹, Yuya Mizuno¹, Yukihiro Nishioka¹, Fumiko Nakagawa¹, Yoshida Toshihiko², Kawasumi Masaya² (1.Graduate School of Environmental Studies, Nagoya University, 2.Institutes of Innovation for Future Society, Nagoya University)

Keywords:

molecular hydrogen,gabbro,peridotite

In response to recent findings on intense degassing of molecular hydrogen (H₂) in the Bulqizë ophiolite, Albania (Truche et al., 2024), we surveyed concentrations of molecular hydrogen precisely in the lower air of Mt. Apoi made of peridotite and gabbro in the Horoman peridotite complex, Hokkaido, Japan. During the first survey done on October 20, 2024, we measured concentrations of hydrogen in the lower air continuously using a hydrogen sensor while walking along its hiking trail and found anomalous enrichment of hydrogen up to 0.1 ppm higher than those in the background air, at the geologic contact between gabbro and peridotite. On the other hand, we could not find any significant anomalies at the other area along the trail of Mt. Apoi most of which consisted of peridotite. To verify the results further, we revisited Mt. Apoi on September 5, 2025, and found anomalous enrichment of hydrogen again, up to 0.4 ppm higher than those in the background air, at the same site we found anomalous enrichment in 2024. While we monitored concentrations of both carbon dioxide (CO₂) and hydrogen sulfide (H₂S) simultaneously, none of them showed correlation with hydrogen concentration, implying that neither exhaust nor hot spring were the source of hydrogen. We also took air samples of the site in a pre-evacuated glass bottles and verified the results obtained by the hydrogen sensor further, through the measurement on the concentrations of hydrogen in the air samples using a mass spectrometer in laboratory. We concluded that there was an emission source of hydrogen in and around the geologic contact. While we further surveyed in and around “the emission site” including the area off the trail, we couldn't locate the precise emission source.
This work was supported by Nagoya University MIRAI Society Project in 2024.