Estimation of the residence time of lake water and spring water around the Mashu volcano

Abstract

Lake Mashu which is the closed lake in Japan located in the east of Hokkaido was formed by the accumulation of water in the caldera area depressed by the eruption of Mashu volcano about 7, 000 years ago. In this lake, transparency of 41.6 m was observed in 1941. The seepage water of the closed lake is considered that is recharged the surrounding groundwater as a part of origin. This study is carried out to make clear the residence time of lake water in Lake Mashu and spring water around the Mashu volcano.