Study on Comparative Assessment of Water Environment around Volcanoes Focusing on Surface Water Quality -Case studies in volcanic areas around Japan-

1. Introduction
There are many volcanoes in the Japanese archipelago, and their formation factors and magma composition vary from volcano to volcano. Due to these differences in characteristics, it is expected that the water quality of rivers and springs around volcanoes will also differ. Based on the results of the measurement and analysis of river water quality in volcanic areas such as Mt.Tokachi, Mt.Asama, Mt.Kusatsu-Shirane, Mt.Ontake, Mt.Hakone, and Shinmo-dake where surveys and water sampling were conducted, we compared water quality in the water environment around each volcano and tried to understand the relationship between the characteristics of volcanoes and water quality.

2. Overview of the target area and survey/analysis methods
The target volcanoes were Mt.Tokachi, Mt.Kusatsu-Shirane, Mt.Asama, Mt.Ontake, Mt.Hakone, and Mt.Shinmoe. Each of these sites was surveyed several times to several dozen times, with frequency ranging from monthly to half a year, for several years. Water temperature, pH (RpH), electrical conductivity (EC), flow rate, COD, etc., as well as TOC (total organic carbon) and major dissolved constituents were measured in the field.

3. Results
The electrical conductivity (EC) values were generally low in the rivers around Ontake, and some rivers in Mt.Kusatsu-Shirane showed EC similar to that of the surrounding hot spring water due to the influence of the underground hydrothermal system. Mt.Tokachi, Mt.Kusatsu-Shirane, Mt.Hakone, and Mt.Shinmoe, and especially Mt.Kusatsu-Shirane and Mt.Hakone have rivers with values exceeding 3,000μS/cm. Since EC is affected by the recent eruption history, surrounding land use, wind-transported salt, and other factors, we will examine the effects of each of these factors to determine the influence of geological formation age and underground eruptive activity on the surface water quality of the volcanoes. The results suggest the possibility that the geological formation age and subterranean eruptive activity may have an impact on the surface water quality.

4. Conclusion
Based on the results of surface water quality analysis at volcanoes, we compared the characteristics of the water environment between volcanoes and attempted to understand the relationship between volcanic activity and surface water quality. The relationship between final volcanic activity (magmatic eruptions) at volcanoes and EC values around volcanic bodies shows a certain correlation, but it is suggested that the quality of surface water is affected by volcanic activity depending on the development of hydrothermal systems at each volcano and the most recent volcanic activity. In the future, we would like to explore methods for comparative research between volcanoes, paying attention to the effects of land use and wind-blown salt around volcanoes, and focusing more deeply on the relationship between dissolved constituents and volcanic activity.