Lake Shikotsu 3.68

is a caldera lake in Chitose, Hokkaidō, Japan. It is a part of the Shikotsu-Toya National Park.GeographyLake Shikotsu is located in the south-west part of Hokkaidō. It has an average depth of 265m and a maximum depth of 363m, making it the second deepest lake in Japan, after Lake Tazawa. It is the 8th-largest lake by surface area in Japan and the second largest of Japan's caldera lakes, surpassed only by Lake Kussharo. It is surrounded by three volcanos: Mount Eniwa to the north and Mount Fuppushi and Mount Tarumae to the south. The caldera formed in the holocene when the land between the volcanos subsided.Due to its depth, the volume of Lake Shikotsu reaches 3/4 of the volume of Lake Biwa, Japan's largest lake, despite of having only 1/9 of that lake's surface area. Due to the small surface area to depth ratio, the water temperature remains quite constant throughout the year, making it the northernmost ice-free lake in Japan. The Bifue, Okotanpe, Ninaru and Furenai rivers feed into it, and its main outlet is the Chitose River.GeologyThe caldera on which Lake Shikotsu sits was formed 40 to 50 thousand years ago. According to the Global Volcanism Program, the caldera was formed 31 to 34 thousand years ago by one of Hokkaidō's largest quaternary eruptions. The caldera consists mainly of dacite, rhyolite, and andesite. The volcanoes Mount Tarumae, Mount Eniwa, and Mount Fuppushi formed on the rim of this caldera.