Most of the West's lakes are crater lakes formed from collapsed volcanoes. Such lakes exist at Balent, Banéfo, Doupé, and near Foumban. Many of these still have active volcanoes at their bottoms, particularly in the northwest on the Western High Plateau. One example is Lake Baleng, northeast of Bafoussam, and the twin lakes of Foumbot. These volcanoes can cause deposits of gas to build up at the lakebed until poisonous gases finally bubble to the surface. Such an eruption at Lake Monoun killed 37 villagers near Foumbot on 15 and 16 August 1984.