Oldoinyo Lengai, Tanzania

Oldoinyo Lengai, seen from Lake Natron.  (Image:  Clem23)

Oldoinyo Lengai, seen from Lake Natron. (Image: Clem23)

The name given to this volcano in the East African Rift system means “Mountain of God” in the Masai language, but we could also call it “Special Snowflake.”

This is the only active volcano in the world that sometimes erupts white lava (note: because of its chemical composition, this lava does turn black when exposed to water during weathering).

It’s more runny than water and has such a low temperature, relatively speaking (500 degrees Centigrade compared to 1200 degrees at, say, Kilauea in Hawaii), that you can’t see it glow in daylight.

Geologists call this unusual lava natrocarbonatite. Translated into English, that means it’s made of sodium (and potassium) carbonate minerals instead of the silicon-based minerals that are good enough for the rest of Earth’s active volcanoes and most of the planet’s outer crust.

A "special snowflake," indeed!  (Image:  Wikipedia)

A “special snowflake,” indeed! (Image: Wikipedia)

Flamingos and Ancient Man

Despite having a name that’s hard for English speakers to pronounce, and its very weird behavior, Lengai is close to two places that are probably very familiar to you.

Lake Natron is that steaming pink salt lake in East Africa you’ve seen on TV nature specials, filled with flamingos.

The birds come here because they like the salt-loving microorganisms that thrive in Lake Natron – it’s a diet that turns the flamingo feathers pink. The heat and excessive saltiness at this lake also keep predators away, so the birds can safely nest.

Plate tectonics - why all this seismicity and volcanism is going on in East Africa.  (USGS, via Wikipedia)

Plate tectonics – why all this seismicity and volcanism is going on in East Africa. (USGS, via Wikipedia)

Well, Oldoinyo Lengai is so close to Lake Natron that its avalanches have sometimes flowed right into the water.

The other nearby landmark also used to be a lake, millions of years ago.

Interbedded layers of lake sediments and ash from Lengai – it does also erupt “normal” stuff – and other volcanoes buried and preserved a detailed history of the ancient life that thrived there.

Then, hundreds of thousands of years ago, seismic activity diverted the streams that fed this lake and it slowly dried up.

Eventually new streams formed and cut down through the old lake’s layers, exposing the fossils in them and forming a gorge that moderns humans first called Oldupai – Masai for a sisal plant that grows there.

Humans being humans, we then misspelled the word, and now this site is world famous as Olduvai Gorge.

Through a Geologist’s Eyes

Here’s a cool video that shows you a lot about Oldoinyo Lengai, as if you were out in the field looking over the geologist’s shoulder.

If you’re a rockhound or nerd, you will also like some of the technical stuff.

Definitions for some terms:

  • Stratovolcano – The “pointy” kind of volcano most people think of first.
  • Angle of repose – How high you can pile something before it collapses. Oldoinyo Lengai has had typical silica-based explosive eruptions – that’s why it’s a stratovolcano – but its unusual natrocarbonatite lava flows have cooled quickly and cemented the mountain’s walls so much that its angle of repose is steeper than it should be. Eventually it will collapse in a debris avalanche, a/k/a landslide. The geologist climbed over the remains of past avalanches and got evidence of a minimum age of 793,000 years for Oldoinyo Lengai. After each avalanche, more eruptions build up a new cone; the current edifice is believed to be some 340,000 years old.
  • Tuff – Yes, it’s often cool, too. Tuff is volcanic debris that has turned to stone.
  • Tephra – Any volcanic debris that’s airborne. If it reaches the ground still hot enough to weld together, tephra will turn into tuff.

More information.

Monitoring at Oldoinyo Lengai is scarce, though there are villages in the area, and Nairobi, Kenya, is about 100 miles away.

There are no webcams.

More information on carbonatites (including pictures of nonglowing lava erupting during the day at Oidoinyo Lengai).

Categories: Sunday morning volcano, volcanoes

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