Ol Doinyo Lengai (Oldoinyo 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, Africa. Part of the volcanic system of the East African Rift, it uniquely produces natrocarbonatite lava. The 1960 eruption of Ol Doinyo Lengai led to geological investigations that finally confirmed the view that carbonatite rock is derived from magma.
The last bigger eruption was in 1966, with some smaller ones in 1983, 1933, and 2007. Ol Doinyo Lengai is one of the few volcanoes without Sodium carbonate and potassium and it is the only volcano in the world that erupts natrocarbonatite lava. This lava has almost no silicon and its temperatures are not as high as those of other lavas, approximately 500 – 600°C.
The volcano has more than one active center and most of the recent eruptions were from its northern crater. Subsidiary cones extend out from the center and down its sides.
The fertile lower levels of the Ol Doinyo Lengai are planted in vineyards and citrus. The steep higher slopes are covered with oak, birch, and beech. Above 6,500 feet a few plants are found scattered among ashes, sand, and fragments of lava and slag.
The natrocarbonatite lava looks like fluid black oil and it turns white when in contact with objects full of moisture. This whitening happens almost immediately when raining. The mountain has two summit craters. The southern one is inactive and filled with volcanic ash. The active one is the northern summit crater, with a depth of over 200 meters. Mount Lengai can be climbed up to the peak and sometimes also all the way down to the crater, almost to the brim of the molten lava flows.
Climbs are mostly organized after midnight to reach the summit in the sunrise. Although the route is hard because of the heat ( 40°C) and hikers are advised to be extremely cautious, the views from Mount Lengai are astonishing. In the north, Lake Natron is visible, in the west the Great Rift Valley, and the eastern part offers majestic views of Mount Kilimanjaro.