Overlooking Lake Natron and the bush-land of Kenya to the north, Oldonyo Lengai, which means "home of God, Or God's Mountain" in Maasai, is an active volcano and one of Tanzania's most spectacular and undiscovered climbs.
The volcano erupts sporadically, sending streams of grey lava down the crater rim and spitting hot ash high into the air. The climb, undertaken overnight so hikers can experience sunrise over the rift valley escarpment is high challenging.
The summit of this strato-volcano is 2962 metres above sea level, and affords direct views into the caldera of Tanzania's only officially-certified active volcano, and the world's only carbonatite volcano; records of eruptions have been maintained since 1883, the largest of which deposited ash 100 kilometres away in Loliondo on the Kenyan border to the north west.
Recent volcanic activity began on 12th July 2007 with daily tremors in Kenya and Tanzania, the strongest of which measured 6.0 on the Richter scale. The mountain finally erupted on September 4, 2007, sending a plume of ash and steam at least 18 kilometres downwind and covering the north and west flanks in fresh lava flows.
The eruption continued intermittently into 2008, with a major outburst taking place on March 5 2008, and smaller eruptions on 8 and 17 April 2008; activity continued until late August 2008. A visit to the summit in September 2008 discovered lava emission from two vents in the floor of the new crater; by April 2009 this activity appeared to have ceased, but eruptions occurred again in October 2010.
A visit to the summit of Oldoinyo Lengai in February 2012 revealed extensive crack development across the summit, accompanied by significant gaseous release. Intermittent noises were detected from the ash pit, and large extents of the rock-studded pavement resounded hollow on percussion, suggesting gaseous build-up beneath the pavement.
The lava of Oldoinyo Lengai is carbonatite-based, rich in nyerereite and gregoryite. These sodium and potassium carbonates mean that the lava erupts at relatively low temperatures, around 500-600ºC, giving the lava a black/muddy appearance in sunlight, as opposed to the reddish hue of the higher-temperatures (1100ºC) of the silicate/basaltic lavas.
Carbonatite lava is the most fluid lava in the world, much less viscous than silicate lavas, and is often more fluid than water. The minerals formed by this lava are very unstable in earth's atmosphere, and rapidly turn from black to grey/white in colour when exposed to moisture. The resultant rock formations are extremely friable, creating a shifting landscape of hard pavements alternating with knee-deep ash. The resulting scenery is different from any other volcano, as Oldoinyo Lengai is the only known active carbonatite volcano in the world.