Ol Doinyo Lengai

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Ol Doinyo Lengai, Tanzania
Ol Doinyo Lengai, Tanzania / Michael Rückl, / CC BY-SA 3.0

There is only one volcano in the world which is erupting carbonatite lava: Ol Doinyo Lengai in Tanzania. This is not just another dry fact for nerdy scientists: this volcano is very unusual place without analogues in the world.

History

The volcano is some 370 thousand years old and is the youngest volcano in this part of the East African Rift.

Of course, local people noticed this giant volcano which is rising tall above the dry plains south from Lake Natron. Here, in East African Rift are located many magnificent volcanoes – not too far are the magnificent Mount Meru and Ngorongoro Crater. But this volcano was very special to Maasai people – it was a sacred place named "Mountain of God" (Ol Doinoy Lengai).

This part of Africa was one of the last places reached by white people – first European visitors to Ol Doinyo Lengai were German explorers in the late 19th century.

This volcano is very active – every few years here takes place an eruption.

Ol Doinyo Lengai volcano, Tanzania
Ol Doinyo Lengai volcano / Richard Mortel, / CC BY 2.0

One of these eruptions in 1960 attracted the attention of Canadian geologist John Barry Dawson who was mapping this part of Tanzania. He and Ray Pickering descended in the crater of volcano (this was the first known descent in the crater) in October 1960 and immediately noticed that this volcano is very unusual. Soon after, in 1962 there was published his research – and the first and only active carbonatite volcano on Earth was discovered.

Since then Ol Doinyo Lengai has been a "playground" for geologists exploring this unique natural wonder. Dawson himself continued the research until his decease in 2013.

Today volcano is rather popular tourist attraction. Fittest visitors are ascending the mountain under the heat of the equatorial Sun and try to get closer to live volcanic activity. This is dangerous – this weird volcano is even less predictable than others and threats are looming in seemingly calm places.

Carbonatite lava

Nearly all volcanoes on Earth are spewing lavas which consist of silicate minerals. Only some have been erupting lava which per more than 50% consists of carbonate minerals – carbonatite lavas. There are known some 20 locations of former carbonatite volcanoes but Ol Doinyo Lengai is the only one which is active now.

"Mountain of God" is erupting not just carbonatite lava – it is producing very specific, rare kind of it: natrocarbonatite lava. It consists of carbonate minerals – the very rare nyerereite (Na2Ca(CO3)2) and gregoryite (Na2,K2,Ca)CO3.

This material needs considerably lower temperature for melting – this lava is flowing already at 500 – 600 °C temperature and in the daylight this lava is not even glowing – it is just a flow of pitch black stream. In the night lava glows in orange color. Usual lavas have a temperature of some 1100 °C.

Carbonatite lava is also quite fluid in comparison to common silicate lavas – it is the most fluid lava in the world flowing almost like a water – often faster than a person can run. Flow of this lava looks like dark oil or brown, muddy foam.

Lava of Ol Doinyo Lengai volcano, Tanzania
Lava of Ol Doinyo Lengai volcano, Tanzania / Thomas Kraft, / CC BY-SA 3.0

As the lava hardens, it is pitch black, with glistering crystals in it. But it is not for long: these carbonatite lavas are quickly weathering. In a few hours time the stone turns white due to the moisture. If the weather is dry, lava turns white in a few days time. If the rain is raining – lava becomes white immediately.

This is caused by a chemical reaction similar to a reaction of burnt lime. Due to this both nyerereite and gregoryite are very rare minerals which even in geological collections should be kept in argon atmosphere.

Over the time the white lava turns into brown powder. After few months lava is soft – one sinks in it when walking.

Thus: the landscape of Ol Doinyo Lengai is unique, without analogues in the world.

Volcanic activity

Ol Doinyo Lengai is the only active volcano in Tanzania. It is very active and is erupting lava and ash every few years.

Hornito in Ol Doinyo Lengai crater, Tanzania
Hornito in Ol Doinyo Lengai crater / Thomas Kraft, / CC BY-SA 3.0

Sometimes, when the content of silicates in lava increases, eruptions of volcano become explosive, sometimes starting with impressive lava fountains – such eruption took place in 2007 – 2008. Before these eruptions there happened many earthquakes – even lions left the area and it was also decided to evacuate also people and their cattle in saf distance from the volcano.

During the eruptions in the crater often form hornitos – smaller hills and even towers, which emit the carbonatite lava. Lava sometimes forms short-lived lava lakes.

Since 1983 the lava has gradually filled the crater and now it is filled with carbonatites and it seems that this is endangering the stability of crater rims.

As the carbonatite lava spread over the surrounding plains, it has changed the soil. These grasslands are rich with succulents and serve as pasture for numerous wildebeest calves.

References

  1. Frederick Belton, Ol Doinyo Lengai, The Mountain of God . Accessed on June 26, 2017

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Ol Doinyo Lengai -2.759612, 35.914042   Ol Doinyo Lengai

Coordinates: 2.7596 S 35.9140 E
Categories: Volcanoes
Values: Geology, Visual
Rank: 3
Address: Africa, Tanzania, Arusha, some 19 km south from Lake Natron
Alternate names: Oldoinyo Lengai
Name in Maasai: Ol Doinyo Lengai (The Mountain of God)
Height: 2,890 – 3,188 m (according to diverse sources)

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