Lake Toya

A caldera lake located near Uchiura Bay in southwest Hokkaido. It is the center of Shikotsu-Toya National Park. It has an area of ​​70.7 square kilometers, a circumference of 52 kilometers, and an elevation of 84 meters above sea level and 179.7 meters at its deepest point. Several volcanic activities from the early Quaternary Period of the Cenozoic Era caused a large amount of welded tuff to erupt, causing the caldera lake to collapse. The current doughnut shape was formed by the eruption of the central crater cone Nakajima. Volcanic activity continues to this day, and the Usu volcano's Great Usu and Small Usu, Showa Shinzan, and Meiji Shinzan (Yosomisan), which make up the outer rim of the volcano, were formed by recent activity. The activity of Mt. Usu on August 7, 1977 (Showa 52) caused great damage to the surrounding area due to volcanic earthquakes, erupted pumice and volcanic ash, and mudflows caused by rain. A large amount of ejecta also fell on Lake Toya, and the surface of the lake, which was usually very clear, became covered in pure white.

There are two hot springs, Toyako Onsen and Sobetsu Onsen, on the lakeside, and there is a forest museum on Nakajima where Yezo deer graze. A tourist road goes around the lake, attracting approximately one million tourists per year. The area around the lake has one of the mildest climates in Hokkaido, and is home to rural areas where rice, fruit and vegetable cultivation, and dairy farming are carried out. The lake water breaks through the crater wall in the east, becomes a crater rapids, and flows into the Osaru River, which is used by the Sobetsu and Abuta power plants.

[Narabe Osamu]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

北海道南西部、内浦(うちうら)湾の近くにあるカルデラ湖。支笏(しこつ)洞爺国立公園の一中心。面積70.7平方キロメートル、周囲52キロメートル、水面標高84メートル、最深部179.7メートル。新生代第四紀初期から数次の火山活動で多量の溶結凝灰岩を噴出して陥没しカルデラ湖ができ、その後中央火口丘中島の噴出により現在のドーナツ型となった。火山活動は現在も継続し、外輪山を構成する有珠(うす)火山の大有珠・小有珠、昭和新山、明治新山（四十三(よそみ)山）などは近年の活動によって生じたものである。1977年（昭和52）8月7日の有珠山の活動は、火山地震、噴出した軽石や火山灰、雨による泥流によって周辺に多大の損害を与えた。噴出物は洞爺湖にも多量に降下し、透明度の高かった湖水も表面が真っ白に覆われた。

　湖畔には洞爺湖温泉、壮瞥温泉(そうべつおんせん)の両温泉があり、また中島には森林博物館があって、エゾシカが放牧されている。湖を一周する観光道路も整備されて年間約100万の観光客がある。湖の周辺は、道内でも有数の気候温和な所で、米作、果樹・野菜栽培、酪農の行われる農村地域が展開する。湖水は東部の火口壁を破って火口瀬(らい)となり、長流川(おさるがわ)に注ぎ、壮瞥、虻田(あぶた)の両発電所で利用されている。

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