15:30 〜 17:00
[SGC37-P04] Activities of the Tatun Volcanic Group in norther Taiwan as recorded through fluid geochemistry monitoring
キーワード：Tatun Volcanic Group, recent monitoring of volcanoes, fluid geochemistry
The back-arc extension and magmatic activity caused by post-collisional rifting and the westward Ryukyu subduction system in northern Taiwan formed a series of volcanic islands, such as the Tatun Volcanic Group (TVG), and submarine volcanoes in the Okinawa Trough. Whether the TVG will be active again is a critical issue for the scientific community, as well as the disaster prevention and reduction in Taiwan. Previous studies deployed a new high dense seismic network records to identify the magma reservoirs in the crust of the TVG. However, there is still room for discussion on the geochemical records used to estimate the possible future eruption patterns and affected areas of the Tatun Volcanic Group. In particular, the construction and monitoring of geochemical models need to be improved.
This study collected fumarolic gases and hot spring samples to measure the gas compositions (including 4He, Ar, N2, CH4, H2, O2, SO2, H2S, HCl, CO2, water vapor and helium isotopic ratio) and ion concentrations in spring waters (including Cl-, SO42-, Na+, K+, Mg2+, and Ca2+) of six fumaroles from 2017 to 2021. Based on the results of geochemical indicators and the seismic events, the volcanic activities of the TVG were relatively quiet from 2017 to 2018, but the fumarolic HCl content in this area started increased. In 2019, the number of seismic events increased, and several large-scale seismic events occurred with focuses of more than 3 km depth while the concentrations of fumarolic 4He and HCl increased. The cation concentrations of spring waters started to increase in 2020, in the meanwhile, the number of seismic events peaked in 2020. It was possibly due to the upwelling of deep hydrothermal fluids. On the other hand, the stable variation of helium isotopic ratio in samples may reflect the role of atmospheric fluids taking in the shallow hydrothermal system. In 2021, the number of seismic events decreased, while fluid anomalies were observed constantly. It implied that the pressure in the magma reservoir of TVG had been released and the activities slowed down accordingly. The results suggested that the TVG has been active since 2019, and the possible disasters caused by active hydrothermal activities, such as steam eruptions, and assess the possible range of volcanic eruptions, should be highly emphasized.
This study collected fumarolic gases and hot spring samples to measure the gas compositions (including 4He, Ar, N2, CH4, H2, O2, SO2, H2S, HCl, CO2, water vapor and helium isotopic ratio) and ion concentrations in spring waters (including Cl-, SO42-, Na+, K+, Mg2+, and Ca2+) of six fumaroles from 2017 to 2021. Based on the results of geochemical indicators and the seismic events, the volcanic activities of the TVG were relatively quiet from 2017 to 2018, but the fumarolic HCl content in this area started increased. In 2019, the number of seismic events increased, and several large-scale seismic events occurred with focuses of more than 3 km depth while the concentrations of fumarolic 4He and HCl increased. The cation concentrations of spring waters started to increase in 2020, in the meanwhile, the number of seismic events peaked in 2020. It was possibly due to the upwelling of deep hydrothermal fluids. On the other hand, the stable variation of helium isotopic ratio in samples may reflect the role of atmospheric fluids taking in the shallow hydrothermal system. In 2021, the number of seismic events decreased, while fluid anomalies were observed constantly. It implied that the pressure in the magma reservoir of TVG had been released and the activities slowed down accordingly. The results suggested that the TVG has been active since 2019, and the possible disasters caused by active hydrothermal activities, such as steam eruptions, and assess the possible range of volcanic eruptions, should be highly emphasized.