[A-HW28] 水循環・水環境

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

★Invited Papers

*知北 和久¹、後藤 章夫²、岡田 純³ (1.北海道大学北極域研究センター、2.東北大学東北アジア研究センター、3.気象庁気象研究所火山研究部)

キーワード：火山活動、火口湖、地下熱水系、水収支、化学物質収支、熱収支

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.