Ol Doinyo Lengai (Oldoinyo Lengai), "Mountain of God" in the

Maasai language Maasai (previously spelled ''Masai'') or Maa (; autonym: ''ɔl Maa'') is an Eastern Nilotic language spoken in Southern Kenya and Northern Tanzania by the Maasai people, numbering about 800,000. It is closely related to the other Maa varie ...

, is an active

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

located in the

Gregory Rift The Gregory Rift is the eastern branch of the East African Rift fracture system. The rift is being caused by the separation of the Somali plate from the Nubian plate, driven by a thermal plume. Although the term is sometimes used in the narrow se ...

, south of

Lake Natron Lake Natron is a salt or alkaline lake located in north Ngorongoro District of Arusha Region in Tanzania. It is in the Gregory Rift, which is the eastern branch of the East African Rift. The lake is within the Lake Natron Basin, a Ramsar Si ...

within the

Arusha Region Arusha City is a Tanzanian city and the regional capital of the Arusha Region, with a population of 416,442 plus 323,198 in the surrounding Arusha District Council (2012 census). Located below Mount Meru on the eastern edge of the eastern ...

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

, Africa. Part of the volcanic system of the

East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of ...

, it uniquely produces

natrocarbonatite Natrocarbonatite is a rare carbonatite lava which erupts from the Ol Doinyo Lengai volcano in Tanzania within the East African Rift of eastern Africa. Natrocarbonatite lavas were first documented in 1962, by J B Dawson. Composition Whereas mo ...

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

. The 1960 eruption of Ol Doinyo Lengai led to geological investigations that finally confirmed the view that

carbonatite Carbonatite () is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geochemical verification. Carbonati ...

rock is derived from

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...

Geology

Ol Doinyo Lengai is unique among active volcanoes in that it produces natrocarbonatite lava, a unique occurrence of volcanic carbonatite. A few older extinct carbonatite volcanoes are located nearby, including

Homa Mountain Homa may refer to: Places Ethiopia * Homa (woreda), a district in Oromia Region, Ethiopia Kenya * Homa Bay, a town and a bay on the shore of Lake Victoria in Kenya * Homa Mountain, a volcano near Homa Bay, Kenya Iran * Chal Homa, Mar ...

Lava

Whereas most lavas are rich in

silicate minerals Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually con ...

, the lava of Ol Doinyo Lengai is a carbonatite. It is rich in the rare

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

and

potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

s, nyerereite and gregoryite. Due to this unusual composition, the lava erupts at relatively low temperatures of approximately . This temperature is so low that the molten lava appears black in sunlight, rather than having the red glow common to most lavas. It is also much more fluid than silicate lavas, often less viscous than water. The sodium and potassium carbonate minerals of the lavas erupted at Ol Doinyo Lengai are unstable at the Earth's surface and susceptible to rapid

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...

, quickly turning from black to grey in colour. The resulting volcanic landscape is different from any other in the world.

Ecology

The carbonatite ash spread over the surrounding grasslands leads to a uniquely succulent, enriched pasture. This makes the area a vital stage on the annual

wildebeest Wildebeest ( , , ), also called gnu ( or ), are antelopes of the genus ''Connochaetes'' and native to Eastern and Southern Africa. They belong to the family Bovidae, which includes true antelopes, cattle, goats, sheep, and other even-toe ...

migration, where it becomes the nursery for the birth of several thousand calves.

Eruptive activity

1883-1915

The record of eruptions on the mountain dates to 1883. Flows were recorded between 1904 and 1910 and between 1913 and 1915.

1917

A major eruption in June 1917 deposited volcanic ash up to away.

1926

An eruption took place for several months in 1926.

1940

An eruption between July and December 1940 deposited ash as far as Loliondo, away.

1950s

Several minor eruptions of lava were observed in 1954, 1955, and 1958.

1960s

Minor eruptions of lava were observed in the early 1960s. A major eruption occurred on 14 August 1966. Geologists J. B. Dawson and G. C. Clark visited the crater a week later and reported seeing "a thick column of black ash" that rose for approximately above the volcano and drifted away northwards towards Lake Natron. When they climbed the cone-shaped vent, they reported seeing a continuous discharge of gas and whitish-grey ash and dust from the centre of the pit.

2007

Volcanic activity in the mountain caused daily earth tremors in Kenya and Tanzania from 12 July 2007 until 18 July 2007 at 8.30pm in

Nairobi Nairobi ( ) is the capital and largest city of Kenya. The name is derived from the Maasai phrase ''Enkare Nairobi'', which translates to "place of cool waters", a reference to the Nairobi River which flows through the city. The city proper ...

. The strongest tremor measured 6.0 on the

Richter scale The Richter scale —also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale—is a measure of the strength of earthquakes, developed by Charles Francis Richter and presented in his landmark 1935 ...

. Geologists suspected that the sudden increase of tremors was indicative of the movement of magma through the Ol Doinyo Lengai. The volcano erupted on 4 September 2007, sending a plume of

ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non-gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...

and

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporizatio ...

at least downwind and covering the north and west flanks in fresh lava flows.

2008

The 2007 eruption continued intermittently into 2008. At the end of February it was reported to be gathering strength, with a major outburst taking place on 5 March. Periods of inactivity were followed by eruptions on 8 and 17 April. Eruptive activity continued until late August 2008. A visit to the summit in September 2008 discovered that lava emission had resumed from two vents in the floor of the new crater. Visits to the crater in March/April 2009 showed that this activity appeared to have ceased.Ol Doinyo Lengai, The Mountain of God
Website maintained by Frederick A. Belton.

2010

In October 2010, two separate lava flows and a small lava lake were photographed in an overflight.

2013

The volcano resumed natrocarbonatite lava flow which started to fill the large crater from the 2007-2008 eruption. As of July 2013, there is a large active

hornito Hornitos are conical, or pipe-like, structures built up by lava spattering or being ejected through an opening in the crust of a lava flow. Hornitos are similar to spatter cones but are rootless, meaning they were once a source of lava but th ...

on the western edge of the crater floor. During June, residents near the volcano reported several earthquakes. The new crater is inaccessible and climbers have only occasionally glimpsed into it.

Gallery

Image:Aerial view of Ol Doinyo Lengai erupting in 2008.jpg, Ol Doinyo Lengai erupting in March 2008. Image:Ol Doinyo Lengai After Explosive Eruptions.jpg, Ol Doinyo Lengai after an explosive eruption. Image:Plume from Ol Doinyo Lengai.jpg, Image of the volcano sending a plume of ash and steam southward. Image:OldoinyoLengaiAir.jpg, Aerial photo of Oldoinyo Lengai in 2011. Image:Ol Doinyo Lengai.jpg, Ol Doinyo Lengai in October 2011. File:Oldoinyolengai.jpg, Image of 1966 eruption File:Lava lengai.jpg, Solidified lava in the crater of Ol Doinyo Lengai. File:Crater of Ol Doinyo Lengai (Jan 2011).jpg, Crater of Ol Doinyo Lengai in January 2011.

Notes

References

External links

Ol Doinyo Lengai at nationalgeographic.com

Ol Doinyo Lengai at Stromboli Online

Ol Doinyo Lengai at Volcano World

St Lawrence University ''Oldoinyo Lengai''

''Fred Belton's Ol Doinyo Lengai site''

''Ol Doinyo Lengai Photos 2001''

Video of molten carbonatite lava flow eruptions at Ol Doinyo Lengai volcano
{{Authority control Carbonatite occurrences Volcanoes of the Great Rift Valley Stratovolcanoes of Tanzania Mountains of Tanzania Active volcanoes Geography of Arusha Region Pleistocene stratovolcanoes Holocene stratovolcanoes