Mount Ol Doinyo Lengai

Rising to an altitude of 9717 feet (2962 meters, though these measurements vary according to different scientists), the symmetrical, steeply-sided, and still active volcano of Ol Doinyo Lengai is located in the Eastern Rift Valley of remote northern Tanzania. Soaring 6562 feet (2000 meters) above the parched and rocky desert floor, it is considered the home of the Masai god, Eng'ai, who occasionally signals her wrath with eruptions and drought. Pronounced ol doyn-yo len-guy, meaning 'Mountain of God' in the Masai language, it has long been a place of pilgrimage for Tanzania's pastoralists, who pray for the most important things in their world: rain, cattle, and healthy children. In one of the more common rituals, Masai elders lead groups of barren women to the mountain's base, where they pray to Eng'ai to bless them with children.

Described by geologists and volcanologists as a classic stratovolcano, it is famous for its unique type of natrocarbonatite lava and, as such, is the only known active natrocarbonatite volcano on earth. The present-day cone, first described in writing by German explorers near the end of the 19th century and dating to approximately 15,000 years ago, was first recognized for its geological uniqueness as recently as 1960. Natrocarbonatite lavas emerge from the earth at significantly lower temperatures (around 500 Celsius) than normal silicate lavas (around 1200 Celsius), and their weak incandescence can only be observed at night. Because of its peculiar chemical composition, natrocarbonatite lava is more fluid than silicate lava and is black or dark brown rather than red. Flowing or bubbling natrocarbonatite lava looks much like black mud and early visitors to the crater mistook it for such.

The natrocarbonatite lava of Ol Doinyo Lengai is composed of minerals that react rapidly with the water and oxygen in the atmosphere. The dark brown or black lava changes, first to grey and pale brown and eventually to almost white. The color change from black to white can occur within a few months, and in rainy weather, the lava surface turns white immediately. At the same time, the texture of the rock changes from hard to soft and crumbly. New flows and volcanic cones are formed, overlapping and covering the older ones, and gradually, the crater floor of the volcano fills up with progressively younger lava. From a distance, non-geologists sometimes assume the mountain is covered in snow, but this is merely the decomposed natrocarbonatite lava.

The historical record of eruptions on Ol Doinyo Lengai dates to 1883, and flows were recorded between 1904 and 1910 and between 1913 and 1915. A major eruption occurred in June 1917, resulting in volcanic ash being deposited about 48 kilometers away. A similar eruption occurred for several months in 1926 and between July and December 1940, resulting in the ash being deposited as far as Loliondo, which is 100 kilometers away. Several minor eruptions of lava were observed in 1954, 1955, 1958, 1960, 1967, 1983, 1994, 2006, 2007-ongoing.

Some people climb Ol Doinyo Lengai every year. While it is not a technical climb requiring equipment, it is a demanding and often dangerously steep walk that takes fit people a whole day to complete. There is no public transport to the mountain, so it is necessary to hire a four-wheel drive vehicle or go with a commercial tour company based in the city of Arusha. Given the mountain's remote location and the deeply gullied, sometimes impassable ravines of the lower slopes, it is suggested that climbers use the service of reputable tour companies in Arusha. Camping near the summit is possible in the relatively safe inactive southern crater or even in the active crater itself. Tour companies will be able to provide the necessary camping equipment.