5:15 PM - 7:15 PM
[SVC32-P21] Continuous monitoring of the CO2/H2S ratio in volcanic gas at Hakone volcano
Keywords:volcanic gas, Hakone volcano, Continuous monitoring, CO2/H2S ratio
In 2015, a small phreatic eruption occurred at Owakudani in the Hakone Volcano in central Japan. Some researchers reported that temporal variation of the concentration ratio of carbon dioxide to hydrogen sulfide in volcanic gases (CO2/H2S ratio) linked to crustal deformation and an increase in the number of earthquakes caused by the volcanic activity (Ohba et al., 2019; Mannen et al., 2021). The problem with conventional methods of monitoring volcanic gas composition is that they require on-site surveys, so they have low time resolution. The present study aims to construct and operate a continuous monitoring system with high time resolution for volcanic gas composition (CO2 and H2S).
The installation site of our monitoring system was the Kamiyu fumarolic area located about 300 m north of Owakudani in Hakone volcano. Toyama et al. (2023) showed the configuration of the continuous observation system and the observation conditions. CO2 and H2S concentration were measured using a non-dispersive infrared absorption analyzer (LI-840A, LI-COR Inc.) and a controlled potential electrolysis sensor (KHS-5P, Komyo Rikagaku Kogyo Co.), respectively. Volcanic gases were introduced for 10 minutes per hour.
Previous research has pointed out that CO2 and H2S volcanic gases in the Owakudani area are derived from magma and hydrothermal systems, respectively (Ohba et al., 2019). The CO2/H2S ratios ranged from 20 to 95, corresponding to that obtained by the conventional detector tube method, indicating that the values obserbed by the developed monitoring system are valid. Significant CO2/H2S ratio fluctuations were observed in April 2023 (Period 1) and from July to December 2023 (Period 2). In Period 1, the CO2/H2S ratio increased from 45 to 95 between early April and mid-April and decreased to 40 in late April. In Period 2, the CO2/H2S ratio increased from 40 to 85 between July and October and decreased to 50 in December. During these periods of fluctuation, there was no significant change in H2S concentration, and an increase in CO2 concentration was observed, indicating the possibility of involvement of magma-derived gases.
The CO2/H2S ratio temporal variation was compared with the data of GNSS (Global Navigation Satellite System) and earthquake activity. No crustal deformation was observed during Period 1, but earthquakes increased immediately after Period 1. On the other hand, the timing of the increase in the CO2/H2S ratio during Period 2 was linked to volcano inflation observed by GNSS. These discrepancies may reflect the factors that caused the increase in the CO2/H2S ratio observed in Period 1 and Period 2.
References: Ohba et al. (2019) EPS, 71, 48.; Mannen et al. (2021) EPS, 73, 80.; Toyama et al. (2023) JpGU2023, SVC33-P06.
The installation site of our monitoring system was the Kamiyu fumarolic area located about 300 m north of Owakudani in Hakone volcano. Toyama et al. (2023) showed the configuration of the continuous observation system and the observation conditions. CO2 and H2S concentration were measured using a non-dispersive infrared absorption analyzer (LI-840A, LI-COR Inc.) and a controlled potential electrolysis sensor (KHS-5P, Komyo Rikagaku Kogyo Co.), respectively. Volcanic gases were introduced for 10 minutes per hour.
Previous research has pointed out that CO2 and H2S volcanic gases in the Owakudani area are derived from magma and hydrothermal systems, respectively (Ohba et al., 2019). The CO2/H2S ratios ranged from 20 to 95, corresponding to that obtained by the conventional detector tube method, indicating that the values obserbed by the developed monitoring system are valid. Significant CO2/H2S ratio fluctuations were observed in April 2023 (Period 1) and from July to December 2023 (Period 2). In Period 1, the CO2/H2S ratio increased from 45 to 95 between early April and mid-April and decreased to 40 in late April. In Period 2, the CO2/H2S ratio increased from 40 to 85 between July and October and decreased to 50 in December. During these periods of fluctuation, there was no significant change in H2S concentration, and an increase in CO2 concentration was observed, indicating the possibility of involvement of magma-derived gases.
The CO2/H2S ratio temporal variation was compared with the data of GNSS (Global Navigation Satellite System) and earthquake activity. No crustal deformation was observed during Period 1, but earthquakes increased immediately after Period 1. On the other hand, the timing of the increase in the CO2/H2S ratio during Period 2 was linked to volcano inflation observed by GNSS. These discrepancies may reflect the factors that caused the increase in the CO2/H2S ratio observed in Period 1 and Period 2.
References: Ohba et al. (2019) EPS, 71, 48.; Mannen et al. (2021) EPS, 73, 80.; Toyama et al. (2023) JpGU2023, SVC33-P06.