Photo of Lengai © Celia Nyamweru

A pahoehoe lava flood, © Fred Belton

Photo © Fred Belton

Photo © Tom Pfieffer

Natrocarbonatite Lavas
Carbonatites contain more than 50% carbonate minerals and are generally intrusive igneous rocks that act as plugs, dykes, and cone sheets. Ol Doinyo Lengai is unusual in that it is extrusive carbonatite. Also, rock near Lengai is generally alkali, and have high levels of sodium and potassium. This is why it is called natrocarbonatite. Few other carbonatites contain these elements. The predominant minerals in these lavas are nyererite and gregoryite, which are anhydrous so they react very quickly with the water in the atmosphere when they reach the surface.
Lava flows like black water out of Lengai; only during night eruptions does the lava glow red. The change in color from black to white is a result of the sodium and potassium reacting with water and takes place over a period of a few months. Because it flows at such low temperatures, it can look like bubbly mud even though it is still very hot. This can make it very difficult to recognize, which can be a problem for naive climbers.

Check out another Earlhamite's webpage on Ol Doinyo Lengai: http://www.earlham.edu/~graveti/oldoinyolengai.htm

Natural arch created by explosive activity
© Fred Belton

Lengai by morning, © Fred Belton

Pahoehoe lava on crater floor

Ol Doinyo Lengai
The Mountain of God

Photo © Fred Belton

Location
In the northcentral portion of Tanzania, only 120 km northwest of bustling Arusha, the dusty countryside becomes the impressive home of one of the most interesting volcanoes in the world: Ol Doinyo Lengai. As a stratovolcano, it rises about 9524 feet above sea level next to its neighbor, Lake Natron. It is one of the few active volcanoes in the African Rift Valley.

This area of Tanzania is home to the pastoralist Maasai tribe. While I lived with one of these Maasai families off the base of Lengai, everyone I met stressed to me that Ol Doinyo Lengai is both a blessing and a curse. They believe the mountain to be the home of a god to which they must pray in order to have healthy cycles of weather. Adequate rainfall affects every single aspect of life for these people who make this dry environment their home.

Photo on left © Tom Pfieffer

A "toy volcano"??
World-famous volcanologist Katia Krafft once called Ol Doinyo Lengai a "toy volcano" because its lava was so cool that she could take samples of it with only a spoon. Why is the lava here so cool? It has everything to do with its composition.
Lengai eruptions are characterized by natrocarbonatite lavas--it is the only volcano on Earth that acts in this manner. Typically its eruptions have low silica content. While normal basaltic flows run at about 2000 degrees F, these lavas show temperatures of about 900-950 degrees F.

Photo by Fred Belton

A place to call home
While perhaps to Katia Krafft this mountain was a "toy volcano," to the people who call this environment home, Lengai is no toy. Maasai are often afraid of the volcano and blame it when extreme droughts make life nearly impossible. Because the area is so remote, Maasai rarely receive outside food or supplies. Therefore it is necessary that everything they need to survive be available nearby. As pastoralists, Maasai are herders of thousands of cows and goats. Their diet consists mostly of meat, blood, and milk. The wellbeing of their livestock depends on adequate rain to sustain the grasses. When rain does not come for months on end, Maasai blame the god on Lengai for showing his fury through severe drought.
Although I met only a few Maasai who ventured up the mountain (they warn of its danger), religious leaders sometimes make trips to the top to find answers. There are legends of warriors who attempted to make their way to the top and never returned. Obviously, to these people, the volcano is no toy.

View from Lake Natron, Photo by Jessica Castleberry

Literature Cited

Harmer, R.E. and Gittens, J. 1998. The case for primary, mantle-derived carbonatite magma. Journal of Petrology 39: 1895-1903.

Mitchel, Roger, H. 2000. Expedition to the natrocarbonatite volcano oldoinyo lengai.
(online version) newsletter of the mineralogical association of Canada 63. 9-10.

http://web.umr.edu/~rhagni/ear-ol.html

http://volcano.und.nodak.edu/vwdocs/volc_images/africa/ol_doinyo.html

http://www.volcano.si.edu/world/volcano.cfm?vnum=0202-12=

http://it.stlawu.edu/~cnya/

http://users.bendnet.com/bjensen/volcano/africa/tanzania-lengai.html

http://www.d.umn.edu/~pmorton/geol2300/classnotes/Igneousprocesseslecturepart1.doc

http://www.decadevolcano.net/volcanoes/africa/oldoinyo_lengai/lengai.htm#photos

http://www.volcanodiscovery.com/volcano-tours/volcanoes/africa/tanzania/lengai_volcano.html

Author: Jessica Castleberry
Email mew with questions/comments
Creation/revision date: April 12, 2005

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