Oldoinyo Lengai is the world’s only active carbonatite volcano, situated in northern Tanzania within the Eastern Rift Valley, al 2.751 degrees S, 35.902 degrees E. It forms an isolated symmetrical cone at the southern end of Lake Natron, with a summit elevation of 2,890 m (9,480 ft). Periodic eruptions of ash and lava have been recorded since about 1880, and with increasing precision during this century since 1904. In 1990 a routine expedition to monitor activity levels at the summit led to the discovery of a remarkable cave located in the crater floor, filled with numerous long delicate pale yellow stalactites and stalagmites of unknown composition. Within 100 m there was considerable volcanic activity taking place, and black lava was spraying from a small cone at a height of some 10 m above the crater floor. Due to the regular emission of lava at the summit of Lengai it is unlikely that the cave could have survived intact for more than a few months at most. High internal temperatures and lack of safe access precluded any attempt at entry and sampling of the very unusual and attractive formations within the cave, but a good photographic record was obtained.
Davies, Gordon J..
"Hades" - A remarkable cave on Oldoinyo Lengai in the East African Rift Valley.
International Journal of Speleology,
Available at: http://scholarcommons.usf.edu/ijs/vol27/iss1/6