Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-VC Volcanology

[S-VC35] Mitigation of volcanic disasters - basic and applied researches

Mon. May 27, 2019 3:30 PM - 5:00 PM 105 (1F)

convener:Shinji Takarada(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Mitsuhiro Yoshimoto(Mount Fuji Research Institute, Yamanashi Prefectural Government), Yasuhiro Ishimine(Research and Education Center for Natural Hazards, Kagoshima University), Tomohiro Kubo(National Research Institute for Earth Science and Disaster Prevention), Chairperson:Mitsuhiro Yoshimoto(山梨県富士山科学研究所), Yasuhiro Ishimine(鹿児島大学地域防災教育研究センター)

4:00 PM - 4:15 PM

[SVC35-09] State of river water pollution derived from the recent volcanic activity of Mt Iwo-Yama, Kirishima volcanoes

*Yoshikazu Kikawada1, Haruka Yamamoto2, Wei Deng, Megumi Fukai (1.Faculty of Science and Technology, Sophia University, 2.Graduate School of Science and Technology, Sophia University)

Keywords:Iwo-Yama, Kirishima Volcanoes, Ebino Highland, river water pollution, arsenic

Mt Iwo-Yama belonging to the Kirishima Volcanoes erupted in 2018 for the first time in 250 years. The recent activity of the volcano has a profound effect on the regional economy, especially in the fields of agriculture and tourism. With the phreatic eruption in April 2018, muddy thermal water spouted out from the newly opened vents resulting pollution in the downstream river. As a result, about 1,400 farmers in the downstream area abandoned rice cultivation in 2018.
The muddy water from the newly opened vents is strongly acidic and high in the concentrations of chloride and sulfate with a remarkable amount of arsenic and some kinds of heavy metals. The mud from the vents is mainly composed of grayish argillaceous particles and elemental sulfur suggesting that it is originated from highly-altered zone related to the geothermal reservoir beneath the volcano.
The vents are still busy gushing the muddy thermal water and vapor/steam as of mid-February 2019, ten months after the eruptive events. Based on our continuous investigation, the overflowing water from the vents is constantly strongly acidic (pH <1) and contains a relatively high concentration of arsenic, although the overflow rate is not constant and changes on occasion. The results of our latest chemical analysis show the water contains around 5 mg/L arsenic. Besides, the spring water in the west flank area of the volcano, which is one of the headwaters of the local river, has become strongly acidic with a rise of volcanic activity. That spring water is also one of the reasons for water pollution in the downstream. As a result, even recently the river water pollution in the foot of the volcano is sometimes reported. The river water pollution thus remains as a problem to be solved both environmentally and economically.