Volcanic activity monitoring applying chemical analysis of thermal water: an example of Ebinokogen Ioyama volcano of the Kirishima Volcanic Group, Kyushu, Japan

Abstract

Fumarolic activity at Ebinokogen Ioyama volcano of the Kirishima Volcanic Complex, which was active until the 1990s, temporarily ceased around 2007 but resumed in December 2015, with sediment discharge in April 2017 at the summit area and small eruptions in April 2018 at the south of summit area and a point about 500 m west of the summit area. Chemical analysis of thermal waters from the natural spring at the foot of Ioyama volcano and craters created 2018 eruptions since August 2016 revealed that the Cl/SO₄ ratio was found to be a good indicator of the activity at this volcano. Based on recent observations, volcanic activity may have increased around the summit area from December 2021 to June 2022 by considering the Cl/SO₄ ratio of hydrothermal water as an indicator.