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Oldonyo Lengai : Strangest Volcano on Earth

Ol doinyo Lengai
Oldoinyo Lengai - Tanzania
Size: height of 2,886 m/9,469 ft.
Location: Northern Tanzania, 300 km (190 miles) Northwest of Arusha.

Ol doinyo Lengai (pronounced ol doyn-yo len-guy) is an active volcano in the Eastern Rift Valley, and it is home to the Masai God Eng'ai, who signals her wrath with eruptions and drought. The name means 'Mountain of God' in the language of the Masai people who inhabit this area. Ol doinyo Lengai is a unique and extremely fascinating volcano that towers above the East African Rift Valley in Northern Tanzania, just south of Lake Natron. It is located on the way between Ngorongoro Crater and the Serengeti and is part of many of our itineraries. Geologists are particularly interested in Ol doinyo Lengai because It is the only volcano in the world that erupts natrocarbonatite lava, a highly fluid lava that contains almost no silicon. Oldoinyo Lengai is also the only active volcano in this part of the Rift Valley, though there are many older extinct volcanoes in this region. The mountain rises a startling 2,886 m/9,469 ft above the parched Rift Valley floor.

Eruption of T58C on July 15, 2004

Referred to as the strangest volcano on Earth, Ol doinyo Lengai earns its reputation when it erupts. Unusually cool, highly fluid lava produces a whimsical world of geologic fantasies that include extrusions frozen in flight. These natrocarbonatite flows have a chemical composition akin to laundry soap, and exposed to the atmosphere, the lava quickly hardens and decays. Unlike common basalt lavas, which are sticky with silica, Lengai’s lavas are mostly slick sodium carbonate with the viscosty of olive oil. Volcanic froth rich in carbon dioxide can spew into the air as liquid lava and harden in midair. Some of the big drops can form little parachutes, and look like silver flying through the air before hitting the ground with the sound of breaking glass. Lengai’s Dr. Seussian formations can crumble a day after they are born, and you can judge their age by their color. Even raindrops accelerate the decomposition.

There is little wildlife on this mountain besides small antelope, reptiles, and insects, but birdlife is quite extensive along the routes.

How To Get There
Ol doinyo Lengai is located between the Serengeti and Ngorongoro along Tanzania's northern circuit. By road, charter or scheduled flight from Arusha, en route to the Serengeti and Lake Manyara.

What To Do
The climb up Ol doinyo Lengai is extremely strenuous, requiring a gain of 1,676 m/5,500 ft. You start the steep 6-hour climb around midnight with the goal of reaching the crater rim for sunrise. Include a visit to Ol doinyo Lengai in your itinerary.  

Ol Doinyo Lengai volcano, altitude 2960 meters (9711 feet), is a unique and extremely fascinating volcano that towers above the East African Rift Valley in Northern Tanzania, just south of Lake Natron.  It is the only volcano in the world that sometimes erupts natrocarbonatite lava, a highly fluid lava that contains almost no silicon. Natrocarbonatite lava is also much cooler than other lavas, being only about 950 degrees F (510 degrees C) compared to temperatures over 2000 degrees F (~1100 degrees C)  for basaltic lavas. Natrocarbonatite is the most fluid lava in the world.  Lava with a low gas content can flow like a whitewater stream, and actually has a viscosity near that of water. Natrocarbonatite lava glows orange at night, but is not nearly as bright as silicon-based lavas since it is not as hot.  

During the day it is not incandescent; most flows look like very fluid black oil, or brown foam, depending on the gas content. In the past, some visitors to the crater believed they were seeing mud flows. Most newly solidified lava is black and contains crystals that sparkle brightly in the sun.  There are also sometimes small flows known as "squeeze-ups" that are light gray when they flow and harden.  

Contact with moisture rapidly turns natrocarbonatite lava white because of chemical reactions that occur when the lava absorbs water.  Eventually the water absorption process turns lava flows into soft brown powder. During dry weather the whitening of flows happens over a period of a few days to a couple of weeks, depending on the thickness of the flow. In rainy weather the lava surface turns white immediately.  In parts of the crater that have been inactive for several months, the ground is light brown/white and so soft that one sinks into it when walking.

Ol Doinyo Lengai also has phases of explosive activity during which the composition of the lava may contain much more silicate material, reducing its viscosity.  In this type of eruption there is no fluid lava and activity takes the form of ash eruptions accompanied by ejection of blocks and bombs.  However, initial phases of an explosive eruption may include strong lava fountains.  The two most recent explosive eruptions occurred during 1966-1967 and 2007-2008.

Since the mid 1980's, lava flows, and to a much lesser extent, explosive eruptions, have been witnessed by many observers of Ol Doinyo Lengai.  Natrocarbonatite lava eruptions are usually centered in one or more small cones that have been formed on the crater floor by previous eruptions of lava. These eruptions have typically taken the form of open lava pools or lakes that may or may not be overflowing, lava flows issuing from holes or cracks inside or near the base of the cones, or lava splashes or fountains from the summit vents of the cones.  

The activity is not well understood but is thought to be a function of the plumbing of the crater, the level of the lava within the plumbing, and the gas content of the lava.  No one knows what causes the lava to flow out at any particular time or how the various vents in the crater are interconnected.  Mineralogists would like to understand how the lava evolves under the surface and why it has its unusual chemical composition, but that also is unknown, although there are several theories.  Finally, no one has any idea why the pattern of frequent small lava flows gave way to explosive activity at the end of August 2007 and how that may have related to earthquakes in the region during the previous two months.

Eruption of T58C on July 15, 2004