Ol Doinyo Lengai, “Mountain of God” in the Maasai language is an active volcano located in the Gregory Rift, south of Lake Natron within the Arusha Region of Tanzania. Part of the volcanic system of the East African Rift, it uniquely produces natrocarbonatite lava. Its major eruption in June 1917 deposited volcanic ash up to 48 kilometers (30 miles) away.
A major eruption occurred on 14 August 1966. Geologists J. B. Dawson and G. C. Clark visited the crater a week later and reported seeing “a thick column of black ash” that rose for approximately three thousand feet above the volcano and drifted away northwards towards Lake Natron. When they climbed the cone-shaped vent, they reported seeing a continuous discharge of gas and whitish-grey ash and dust from the centre of the pit.
Ol Doinyo Lengai also has phases of explosive activity during which the composition of the lava may contain much more silicate material. With this type of eruption, initial phases of the eruption may include strong lava fountains but usually there is no fluid lava and ash eruptions accompanied by ejection of rocks and explosions occurs. The two most recent eruptions of this type occurred during 1966-1967 and 2007-2008. Almost without fail, about every seven years Lengai erupts and plumes of smoke billow out of the crater. At other times it is possible to walk down into the crater, almost to the edge of the molten lava flows.
Views in the north from its summit crater lies the hot barren salt flats of Lake Natron stretch into the distance, beyond lies the Kenyan border. The day temperatures by the lake often exceed 40°C and a few animals survive here with the flamingo making its home here as breeding grounds, nesting on the salty surface on upraised mounds. The view on the east is dominated by Mt Kilimanjaro and to the west the forested escarpments and hills comprising the western slopes of the Great African Rift Valley.