9:00 AM - 10:30 AM
[SVC30-P05] Recent variations in water chemistry of hot water pools and springs at Mt. Iwo, Kirishima volcanoes
Keywords:variations in water chemistry, Mt. Iwo in the Ebino Plateau, hot water pools
A phreatic eruption occurred in 2018 at Mt. Iwo in the Ebino Plateau of Kirishima Volcanoes, and active hydrothermal and fumarolic activity continues today. Signs of increased hydrothermal activity, such as the appearance of new fumaroles and springs, had been observed since 2015, which subsequently led to the eruption. We have been continuously sampling spring water around Mt. Iwo.
Our 2022 water sampling at Mt. Iwo was limited to two sampling events in April and November, both of which coincided with periods of increased seismic activity. The Cl/SO4 content ratios in the hydrothermal pool located at the south side of the summit of Mt. Iwo in the two water samples taken in 2022 were much higher than those in the 2021 samples, suggesting a significant change in hydrothermal activity. The Cl/SO4 molar ratio in November 2022 was about 11, much higher than the highest Cl/SO4 molar ratio of about 2 in January 2019, which was the highest value in our previous observations. Cl and F concentrations showed significant increases in tandem in 2022, suggesting an increased supply of magmatic volatiles from the deeper part. However, As and B concentrations, which showed good correlations with Cl concentrations during the 2018-2019 active period following the eruption, do not appear to have such a clear correlation this time. Therefore, in this 2022 activation, the formation process of fluids supplied to the summit region of Mt. Iwo may differ from that in the 2018 - 2019 period following the eruption.
Our 2022 water sampling at Mt. Iwo was limited to two sampling events in April and November, both of which coincided with periods of increased seismic activity. The Cl/SO4 content ratios in the hydrothermal pool located at the south side of the summit of Mt. Iwo in the two water samples taken in 2022 were much higher than those in the 2021 samples, suggesting a significant change in hydrothermal activity. The Cl/SO4 molar ratio in November 2022 was about 11, much higher than the highest Cl/SO4 molar ratio of about 2 in January 2019, which was the highest value in our previous observations. Cl and F concentrations showed significant increases in tandem in 2022, suggesting an increased supply of magmatic volatiles from the deeper part. However, As and B concentrations, which showed good correlations with Cl concentrations during the 2018-2019 active period following the eruption, do not appear to have such a clear correlation this time. Therefore, in this 2022 activation, the formation process of fluids supplied to the summit region of Mt. Iwo may differ from that in the 2018 - 2019 period following the eruption.