The largely Pliocene Namarunu trachytic shield volcano is topped by cones and lava flows of upper Pleistocene and Holocene age. Voluminous basaltic effusive and explosive activity took place during the early Holocene on the lower N, E, and S flanks along the axis of the East African Rift. The activity produced fissure-controlled subaerial basaltic scoria cones and lava flows, and partially or completely sub-lacustral tuff cones, tuff rings, and pillow lavas. Olivine basalts erupted from a breached scoria cone at the summit. The youngest eruptions postdated the drying out of Lake Sugata about 3,000 years ago. Some could be as recent as the recorded eruptions at The Barrier volcano to the north (Dunkley et al., 1993). Hot springs are located on some of the young volcanic cones on the rift valley floor and on the E side of the rift along the base of the Tirr Tirr Plateau.