Analysis of Hydrothermal Systems Beneath Tayukeng through Long-Term Geochemical Signals of Hydrothermal Fluids in Tatun Volcano Group, Taiwan.

Hsin-Fu Yeh,Hung-Hsiang Hsu

doi:10.3390/ijerph18147411

Abstract

The Tatun Volcano Group (TVG) is located in northern Taiwan and consists of many springs and fumaroles. The Tayukeng (TYK) area is the most active fumarole site in the TVG. In this study, we analyzed the long-term geochemical variations of hydrothermal fluids and proposed a mechanism responsible for the variation in TYK. There are two different aquifers beneath the TYK area: a shallow SO42−-rich aquifer and a deeper aquifer rich in Cl−. TYK thermal water was mainly supplied by the shallow SO42−-rich aquifer; therefore, the thermal water showed high SO42− concentrations. After 2015, the inflow of deep thermal water increased, causing the Cl− concentrations of the TYK to increase. Notably, the inferred reservoir temperatures based on quartz geothermometry increased; however, the surface temperature of the spring decreased. We inferred that the enthalpy was lost during transportation to the surface. Therefore, the surface temperature of the spring does not increase with an increased inflow of deep hydrothermal fluid. The results can serve as a reference for understanding the complex evolution of the magma-hydrothermal system in the TVG.

Highlights

The Tatun Volcano Group (TVG) is located in northern Taiwan and consists of many springs and fumaroles
Long-term geochemistry data of thermal fluids is useful for understanding hydrothermal systems in volcanic areas
We analyzed the variation in the chemical composition of the TYK thermal water between 2004 and 2019

Summary

Introduction

The Tatun Volcano Group (TVG) is located in northern Taiwan and consists of many springs and fumaroles. The Tayukeng (TYK) area is the most active fumarole site in the TVG. After 2015, the inflow of deep thermal water increased, causing the Cl− concentrations of the TYK to increase. The surface temperature of the spring does not increase with an increased inflow of deep hydrothermal fluid. When the gas released from magma interacts with the water, it is preserved as anions in the thermal water. Indicators such as SO4 2 − , Cl− , pH, and the temperature of the thermal water can provide information about volcanic activity [6]. Long-term geochemical variation of the thermal waters is useful for understanding the magmatic-hydrothermal system in volcanic areas. Recent studies have conducted geophysical investigations of the TVG, such as precise leveling [16], gravity monitoring [17], satellite images [18] and seismological observations [19] indicating that

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