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[SVC27-P05] Present situation of water pollution problem caused by 2018 Iwo-Yama volcano eruption in Kirishima volcanic complex
Keywords:Kirishima volcanic complex, Iwo-Yama volcano, phreatic eruption, water pollution, arsenic, thermal water pool
In April 2018, the first eruption in 250 years occurred at the Iwo-Yama volcano of the Kirishima volcanic complex. The newly opened vents with the phreatic eruptions gushed out the strongly acidic hydrothermal fluids containing toxic metal ions like lead and arsenic. The hydrothermal fluids were transported by a river to the Kakuto Basin at the volcano's foot and significantly impacted the agriculture and fishery in the lower reaches. The hydrothermal discharge from the volcano was prolonged, and the water pollution problem in the lower reaches finally came to an end near three years after the eruption. This study reviews the river water pollution in the Sendai River system caused by the 2018 Iwo-Yama volcano's eruption.
The new small craters opened on the south and west sides of the Iwo-Yama volcano summit area in April 2018, causing phreatic eruptions. There was one eruption at each crater, but a large amount of muddy thermal water discharged from the craters flowed into the Akago River, which originated from the area, and was carried to the Nagae River and the Sendai River. At this time, fish carcasses floated up in the river, and farmers had to give up paddy rice cultivation in the river basin. After that, the craters became thermal water pools, and a large amount of water that overflowed continued to be carried downstream, resulting in the water pollution problem in rivers for several years.
In May 2019, a demonstration experiment of a river neutralization system was started in the Akago River, and all river water, including thermal water from the craters of the Iwo-Yama volcano, began to flow down through the neutralization facility. The system works to reduce the solubility of metal ions dissolved in the river water and produces a neutralization product, resulting in a lower concentration of harmful dissolved components. The water quality of downstream rivers has improved significantly since the start of the neutralization demonstration experiment. At first glance thus, it seems that the effect of river neutralization has appeared. However, at that time, the hydrothermal activity of the Iwo-Yama volcano significantly decreased. The decreased activity resulted in lower acidity and lower concentrations of dissolved components in the crater pool. Besides, the amount of overflow from the pool also decreased at the same time. Consequently, it is unclear whether water quality improvement is due to river neutralization or decreased volcanic activity. On the other hand, referring to the data of river water quality monitoring by Miyazaki Prefecture [1], no significant fluctuations have been seen in river water quality in the downstream area since May 2019, which must be the effect of river neutralization.
As of the end of 2020, the Iwo-Yama volcano's volcanic activity is not so active, and there is little hydrothermal overflow from the thermal pool. The water quality of the Nagae River and the Sendai River in the Iwo-Yama volcano's lower reaches is stable and meets the environmental standard.
[1] Results of Water Quality Inspection of Akago River, Nagae River and Sendai River in Ebino City, https://www.pref.miyazaki.lg.jp/kankyokanri/kurashi/shizen/ebino.html (accessed 2021-02-12)
The new small craters opened on the south and west sides of the Iwo-Yama volcano summit area in April 2018, causing phreatic eruptions. There was one eruption at each crater, but a large amount of muddy thermal water discharged from the craters flowed into the Akago River, which originated from the area, and was carried to the Nagae River and the Sendai River. At this time, fish carcasses floated up in the river, and farmers had to give up paddy rice cultivation in the river basin. After that, the craters became thermal water pools, and a large amount of water that overflowed continued to be carried downstream, resulting in the water pollution problem in rivers for several years.
In May 2019, a demonstration experiment of a river neutralization system was started in the Akago River, and all river water, including thermal water from the craters of the Iwo-Yama volcano, began to flow down through the neutralization facility. The system works to reduce the solubility of metal ions dissolved in the river water and produces a neutralization product, resulting in a lower concentration of harmful dissolved components. The water quality of downstream rivers has improved significantly since the start of the neutralization demonstration experiment. At first glance thus, it seems that the effect of river neutralization has appeared. However, at that time, the hydrothermal activity of the Iwo-Yama volcano significantly decreased. The decreased activity resulted in lower acidity and lower concentrations of dissolved components in the crater pool. Besides, the amount of overflow from the pool also decreased at the same time. Consequently, it is unclear whether water quality improvement is due to river neutralization or decreased volcanic activity. On the other hand, referring to the data of river water quality monitoring by Miyazaki Prefecture [1], no significant fluctuations have been seen in river water quality in the downstream area since May 2019, which must be the effect of river neutralization.
As of the end of 2020, the Iwo-Yama volcano's volcanic activity is not so active, and there is little hydrothermal overflow from the thermal pool. The water quality of the Nagae River and the Sendai River in the Iwo-Yama volcano's lower reaches is stable and meets the environmental standard.
[1] Results of Water Quality Inspection of Akago River, Nagae River and Sendai River in Ebino City, https://www.pref.miyazaki.lg.jp/kankyokanri/kurashi/shizen/ebino.html (accessed 2021-02-12)