Oku Volcanic Field

Rocks in the massif have ages from 24.9 to 22.1 million years ago, but more recent activity has occurred.

[3] The massif is composed of rhyolitic and trachytic rock, and contains many maars and basaltic cinder cones.

On 15 August 1984, an earthquake and landslide triggered a major release of carbon dioxide from Lake Monoun, killing several people.

[2] Lake Nyos is inside a maar formed by an explosion about 400 years ago, and is about 1,800 m wide and 208 m deep.

[4] On 21 August 1986, Lake Nyos released a massive amount of carbon dioxide which killed at least 1,700 people by suffocation, possibly triggered by a force 5 earthquake along the Foumban Shear Zone, which runs under the massif.