Ol Doinyo Lengai
Interesting facts
- Its natrocarbonatite is the least viscous lava known, racing downhill at up to about five metres per second in flows only centimetres thick.
- In daylight the cool lava can pass for mudflows or spilt oil; its faint glow becomes visible only after dark.
- According to Maasai myth, the god Engai withdrew to the mountain after being wounded by a hunter's arrow.
- The volcano exhales roughly 80 kilograms of carbon dioxide every second, making it a significant natural source of volcanic CO2.
- Geologists use its carbon-rich magmas as a natural analogue for conditions that might exist on hypothetical carbon planets.
- The symmetrical cone rises more than 1,800 metres above the Gregory Rift and is the only volcano in that branch of the East African Rift currently active.
- An explosive eruption beginning in September 2007 threw an ash column about 3 km high and blasted out a new crater roughly 300 metres wide.
- In the mid-20th century the northern crater was about 200 metres deep; lava gradually filled it and by 1998 was spilling over the rim.
- Ash from an eruption some 2,500 to 3,000 years ago feeds the wind-driven "shifting sands" dunes that creep across the plains near Olduvai Gorge.
- The volcano erupts in Bibhutibhushan Bandyopadhyay's 1937 Bengali adventure novel Chander Pahar, nearly killing its two heroes.
Why it is worth it
Every other active volcano on Earth erupts some form of silicate lava — basalt, andesite, something built around conventional molten rock. Ol Doinyo Lengai is the only one that does not. Its lava is natrocarbonatite, a rare carbonate-rich melt that runs at roughly 500–600°C, hundreds of degrees cooler than typical basaltic lava's 1,100°C-plus. The temperature difference is visible, not just measurable: fresh natrocarbonatite lava looks black or dark brown rather than glowing red, because it simply is not hot enough to incandesce the way lava is expected to.
What happens next is the stranger part. The moment that dark lava is exposed to humidity and rain, the minerals in it react with atmospheric moisture and begin turning white — a mountainside can shift from black to chalk-white within hours, as though the volcano is bleaching itself. Repeated eruptions over time have built up pale, almost lunar-looking terrain near the summit that has nothing to do with ash or snow.
To the Maasai, the mountain's name — "Mountain of God" in the Maa language — is not a marketing description; Ol Doinyo Lengai is considered the home of the god Engai and has served as a pilgrimage site for Maasai pastoralists for generations, independent of its geological novelty. The current eruptive phase began in 2017 and has continued intermittently since, meaning the mountain people visit today is still actively, if slowly, remaking itself.
Getting there
65 km from Mto wa Mbu. Arusha Airport (ARK) is about 104 km away.
On these lists
From the encyclopaedia
Ol Doinyo Lengai is an active stratovolcano in northern Tanzania. It consists of a volcanic cone with two craters, the northern of which has erupted during historical time. Uniquely for volcanoes on Earth, it has erupted natrocarbonatite, an unusually low temperature and highly fluid type of magma. Eruptions in 2007–2008 affected the surrounding region.
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