[A-HW16] Water and material transport and cycles in catchment ecosystems: from headwater to coastal area

[AHW16-P20] Heat budget of hydrothermal ponds and its relation to geothermal flux in a neighboring deep lake: Kuttara Volcano, Hokkaido, Japan

*Kazuhisa Chikita¹, Taiki Shibata² (1.Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, 2.Department of Earth and Planetary Sciences, School of Science, Hokkaido University)

Keywords:hydrothermal flow system, geothermal heat flux, volcanic activity

In order to know the geothermal activity of Kuttara Volcano, Hokkaido, Japan, heat budget of internal hydrothermal ponds is estimated and its geothermal influence on the neighboring deep Lake Kuttara (148 m depth in maximum) is explored. The major hydrothermal area in the geothermal region of Noboribetsu town consists of three hydrothermal ponds, Oh-yunuma (water surface area, 1.61×10⁴ m²), Okunoyu (9.0×10² m²) and Taisho-Jigoku (2.6×10² m²), and a small bubbling pond (4.1 m²), where the bubbling of hot water continuously occurs. Heat budget of Oh-yunuma, Okunoyu and the small bubbling pond in 2013 – 2015 showed mean geothermal flux at 2.8, 22.0 and 32.0 kW m^-2, respectively. It was found out that the neighboring Lake Kuttara increases both water temperature, T (℃), and electric conductivity, EC₂₅ (mS/m), at 25 ℃ near the bottom at the deepest point (148 m) in thermally stratified periods of 2013 - 2015. The linear relationship between T and EC₂₅ suggests that geothermal water leaks to the bottom. The geothermal flux at the bottom was calculated at a range of 0.50 - 9.3 W m^-2 with mean of 2.9 W m^-2. With respect to the interannual geothermal-flux variations, a comparison between Okunoyu and Kuttara indicates that Kuttara responses to the geothermal variation of Okunoyu with a time lag of 5 months on average. Supposing a hydrothermal reservoir at ca. 100 m below the lake bottom, the time lag is explained by the Darcy law between the reservoir and lake bottom.