Ol Doinyo Lengai – Geology, Ecology, Eruption Activity and More

Ol Doinyo Lengai – Geology, Ecology, Eruption Activity and More

Ol Doinyo Lengai (alias Oldoinyo Lengai), which is a Maasai word meaning “Mountain of God”, is an active volcanic mountain within the Gregory Rift, to the south of the Natron Lake, on Tanzania’s Arusha Region. It belongs to the East African Rift Valley‘s volcanic system, and it’s known for producing natrocarbonatite lava. Geological investigations following the eruption of the mountain in 1960 finally proved the theory that carbonatite is magma derived.

Ol Doinyo Lengai Geology

Lava that has solidified at the Ol Doinyo Lengai crater
Lava that has solidified at the Ol Doinyo Lengai crater

The Ol Doinyo Lengai volcano is one of the few active volcanoes that generates natrocarbonatite lava, which is a kind of volcanic carbonatite found nowhere else. Nearby are some older carbonatite volcanoes that are extinct, notably Mount Homa.


Unlike other lavas, which have abundant silicate minerals, Ol Doinyo Lengai’s lava is carbonatite. It contains gregoryite and nyerereite, which are rare potassium and sodium carbonates. The eruption of the lava occurs at comparatively lower temperatures of around 510 degrees celsius (950 °F) because of its unique composition. The volcano’s molten lava looks black when struck by sunlight instead of the usual red glow that lavas have due to its low temperature. It is also a lot more fluid compared to silicate lavas, with viscosities that are typically lower than that of water. The erupted lavas in Ol Doinyo Lengai contain potassium and sodium carbonate minerals, which are unstable on the surface of the Earth and vulnerable to fast weathering, turning grey in color from its original black color. The ensuing volcanic landscape does not resemble anything else on the planet.

Ol Doinyo Lengai Ecology

The produced carbonatite ash has been dispersed throughout the adjacent Ol Doinyo Lengai grasslands resulting in a very succulent and enhanced pasture, making the location a crucial stop on the yearly wildebeest migration since it serves as a nursery for thousands of calves.

Ol Doinyo Lengai Volcanic Activity

1883 to 1915

The Ol Doinyo Lengai mountain’s eruptions have been documented since 1883. Between 1904 to 1910 and 1913 to 1915, flows were documented.


Volcanic ash was deposited about 48 km (30 miles) away during a big eruption in June of 1917.


In 1926, there was an eruption that lasted several months.


Between July to December 1940, an eruption dumped ash as distant as Loliondo, which is 100 km (62 miles) away.

The 1950s

In 1954,55, and 1958, there were several small lava outbreaks.

The 1960s

In the initial years of the 1960s, there were a few minor lava eruptions at Ol Doinyo Lengai.

On August 14, 1966, there was a massive eruption. A week later, geologists G. C. Clark and J. B. Dawson visited the mountain’s crater and saw “thick black ash” rising 1,000 m (3,000 feet) above the mountain and drifting towards Lake Natron to the north. They saw a continual flow of gas, white-grey ash, as well as dust emanating from the pit’s center as they climbed the cone-shaped vent.

Ol Doinyo Lengai 1966 volcano eruption
Ol Doinyo Lengai 1966 volcano eruption


Daily tremors were felt in Tanzania and Kenya from July 12 to July 18, 2007, at about 8.30 p.m. in Kenya’s Nairobi due to volcanic activity in the Ol Doinyo Lengai mountain. On the Richter scale, the strongest tremor was 6.0. The rapid rise in tremors was thought to be due to magma movement through the mountain, as per geologists. On September 4, 2007, the volcano erupted, generating a cloud of steam and ash more than 18 km (11 miles) downwind and lava flows in the west and north flanks.


The Ol Doinyo Lengai eruption in 2007 lasted into 2008, with sporadic recurrences. It was believed to be gaining intensity as February ended, with a significant outburst on March 5. On the 8th and 17th of April, further eruptions occurred after periods of quiet. The eruptions lasted until the end of August 2008. In September 2008, a tour to the volcano’s summit revealed lava emission from 2 vents on the new crater’s floor had restarted. This activity seemed to have ended on follow-up visits in March and April 2009.


An overflight in 2010 October captured two different lava flows at Ol Doinyo Lengai as well as a tiny lava lake.


The Ol Doinyo Lengai volcano has restarted the flow of natrocarbonatite lava that began filling the enormous crater during eruptions that occurred in 2007-2008. On the western border of the crater floor, a big active hornito exists as of 2013 July.  Communities living close to the volcano testified multiple tremors in June. The newly formed crater cannot be accessed, and climbers have only caught a glimpse of it on rare occasions.

For more articles related to Mountains of Tanzania, click here!