[A-HW28] Hydrology and Water Environment

[AHW28-07] A comparative study on hydrothermal conditions of crater lakes under volcanic activity

★Invited Papers

*Kazuhisa A. Chikita¹, Akio Goto², Jun Okada³ (1.Arctic Research Center, Hokkaido University, 2.Center for Northeast Asian Studies, Tohoku University, 3.Department of Volcanology Research, Meteorological Research Institute, Japan Meteorological Agency)

Keywords:volcanic activity, crater lake, underground hydrothermal system , water budget, chemical budget, thermal budget

Two closed crater lakes, Okama and Kananuma, Japan, under volcanic activity were hydrothermally explored. Okama and Katanuma are included in Zao Volcano and Naruko Volcano, Miyagi Prefecture, respectively, of which the activity is at present relatively stable. Hydrological, chemical and thermal budgets of the lakes were estimated by using hydrometeorological, thermal and chemical data obtained in 2023-2024. A water level of Okama varied greatly with the amplitude of more than 4 m, highly responding to snowmelt and rainfall, while that of Katanuma was less sensitive to snowmetl and rainfall with the amplitude of 0.6 m. This suggests that, due to the geology of high permeability for Naruko Volcano, groundwater outflow from Katanuma is highly adjustable to water level. Meanwhile, the low permeability for Zao Volcao appears to produce the dehydrated alteration zone at ca. 300m below the lake bottom, as suggested by the underground AMT resistivity survey. Here, it is also shown that seasonal variations of thermal conditions are greatly different between the lakes.