Lake Nyos (nēōs´), freshwater lake in a volcanic crater in North-West prov., Cameroon, 15 mi (24 km) ENE of Wum. On Aug. 21, 1986, carbon dioxide gas was released from the mineral-saturated waters trapped in the lake's depths, erupting some 260 ft (80 m) high, spreading as far as 12 mi (19 km) away. and suffocating 1,700 people in nearby villages. In 2001 a vertical pipe was lowered into the lake's depths, allowing carbon-dioxide-rich waters to rise to the surface in a controlled fountain. Lake Monoun, to the southeast, is subject to similar eruptions (one occurred in 1984), and water from its depths is also piped to the surface.