[S-GC32] Volatiles in the Earth - from Surface to Deep Mantle

[SGC32-P04] Volcanic Dynamics in Northern Taiwan: Insights from Geochemical Investigations of the Tatun Volcanic Group

*AITI CHEN¹, Hsiaofen Lee², Yuji Sano³, Takanori Kagoshima⁴, Naoto Takahata⁵, Cheng-Horng Lin⁶, Ching-Hua Lo¹ (1.Department of Geosciences, National Taiwan University, Taipei, Taiwan, 2.National Center for Research on Earthquake Engineering, National Applied Research Laboratories, Taipei, Taiwan, 3.Center for Advanced Marine Core Research, Kochi University, Nankoku, Japan, 4.Graduate School of Science and Engineering, University of Toyama, Toyama, Japan, 5.Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan, 6.Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan)

Keywords:Volcanic disaster, Geochemical Monitering, Noble Gases, Gas Geochemistry

The back-arc extension and magmatic activity induced by post-collisional rifting and the westward-migrating of the Ryukyu subduction system in northern Taiwan have given rise to a chain of volcanic isles, including the Tatun Volcanic Group (TVG), and submarine volcanoes in northern Taiwan and within the Okinawa Trough as well. The resurgence of activity in the TVG constitutes a pivotal concern within the scientific community, as well as a paramount subject for disaster prevention and mitigation efforts in Taiwan. Recent investigations have employed an advanced, densely distributed seismic network to discern magma reservoirs embedded in the TVG crust. However, there remains a scope for discourse regarding the geochemical records utilized for predicting potential eruption patterns and delineating affected regions within the TVG. In particular, there is a pressing need for refinement in the construction and monitoring of geochemical models.
The present study amalgamates samples of fumarolic gases from six fumaroles and hot springs, spanning the period from 2017 to 2021, along with ten distinct well water samples obtained 15-20 km away from the presumed magma chamber of TVG. This comprehensive dataset facilitated the analysis of gas compositions (encompassing ⁴He, Ar, N₂, CH₄, H₂, O₂, SO₂, H₂S, HCl, CO₂, vapor water, and helium isotopic ratio) and ion concentrations in spring waters (comprising Cl^-, SO₄^2-, Na⁺, K⁺, Mg²⁺, and Ca²⁺). Geochemical and seismic data point to a relatively dormant phase in Tatun Volcanic Group (TVG) activities during 2017-2018, despite an uptick in fumarolic HCl content. In 2019, seismic events surged, marked by notable deep-focus seismic events and increasing concentrations of fumarolic ⁴He and HCl. Ion concentrations in spring waters also demonstrate an upward trend in 2020, coinciding with heightened seismic activity, possibly linked to the emergence of profound hydrothermal fluids. In 2021, while seismic events decreased, persistent fluid anomalies hinted at reduced pressure in the TVG magma reservoir, leading to subdued volcanic activities. These findings underscore TVG activation since 2019, highlighting the imperative for enhanced monitoring of potential disasters associated with active hydrothermal activities, such as steam eruptions, and a thorough assessment of potential volcanic eruption ranges. This study will evaluate the impact of the magma chamber on surrounding area using the measured data from groundwater samples.