Oldoinyo Lengai is a volcano in the Eastern Rift Valley, North Tanzania. Its name means ‘Mountain of God’ in the language of the Masai people.
Oldoinyo Lengai is of particular interest to geologists because it is the world’s only active volcano that erupts natrocarbonatite lava. It is also the only active volcano in this part of the East African Rift Valley, though there are many older extinct volcanoes in this region. Oldoinyo Lengai rises about 2000 metres above the Rift Valley floor to a height of approximately 2886 metres.