The Chokai Volcano, which lies on the coast of the Japan Sea, is one of the famous volcanoes of the northeast Japan, and Tori-no-umi is the crater lake near the top of this volcano. This is a report of the limnological survey of this lake.
1) This lake has an elliptical shape as is shown by the bathymetric map (Fig. 2).
2) As seen from Figs. 4 and 9, the vertical distribution of the water temperature and the chemical quality shows typical features at the periods of the summer stagnation and the autumnal circulation.
3) The result of the chemical analysis (Tables 2-4) generally reveals that Tori-no-umi is poor in dissolved substances.
4) This lake is characterized by rather high concentration of Na⁺ and Cl^-. (These features are not seen in the several lakes in the Zao and the Shirataka Volcano areas distant from the Japan Sea coast.) The writers inferred that the chemical quality of Tori-no-umi lake is originated from the atmospheric salt in the remaining snow around the lake.