lake Toya

The Toya lake is a lake across the Hokkaido Abuta-gun Doya lake town and the Usu-gun Sobetsu-cho. It is included in Shacdouya national park. It is major power summit (summit) venue of 2008.

The Doya caldera was formed through several-time eruptions at the last interglacial period about 100,000 years ago. The descent volcanic ash by the last large-scale eruption is seen in the stratum within the range wide in which it puts it from Hokkaido on Tohoku. The plateau with the pyroclastic flow deposit is formed around the caldera wall. The lake was polluted by the mine wastewater poured away from the sulfur mine according to the hood that operated from before the war to 1955's as it is by the strong acid like PH2 in 1955's and a lot of living things died out. However, when Mount Usu erupted greatly in 1977, and a large amount of volcanic ash poured down over the Doya lake, it became shape that an acid lake was neutralized by an alkaline volcanic ash, and acidity is eased as a result.