Flows of natrocarbonatite associated with eruptions from the early 1990s could formerly be observed in a shallow summit crater which had remained intact since 1960. The altered, white or pale grey natrocarbonatite ashes that partially cloak the upper slopes resemble an ice cap when seen from distance. The high sodium contant of the natrocarbonatitite lavas and ashes reacts rapidly with meteoric waters to create secondary, white coloured minerals within a few days. The natrocarbonatite is erupted at temperatures considerably lower than silicate lavas. Silicate magmas are the most abundant, but it is the highly unusual natrocarbonatite magmas for which Lengai is so well known. Oldoinyo Lengai is one of the most famous Holocene volcanoes on Earth as it was here the coexistence of two immiscible magmas with radically different compositions was first observed in nature.

(3,188 m) rises some 2.5 km above the valley floor to the southwest of Lake Natron. Natron is an extraordinarily toxic, soda lake (pH of 12) with extensive sodium carbonate salt flats. The lake is bordered to the west by the Western Escarpment, a major rampart constructed of layer upon layer of Pliocene-age volcanic lavas and tephra, and to the east by the giant Gelai Is located in a desolate, relatively low-lying section of the Gregory Rift Valley, northern Tanzania.

Natron salt