Wachacha is a well preserved volcanic dome of some 100 km2 centred about 20 km west-southwest of Addis Ababa. The volcano consists of trachytic flows, tuffs, breccias and possible plugs. The trachytes are probably peralkaline. Carbonate veins and dykes in the summit area were, in the absence of thin sections (P.A. Mohr, pers. comm., 1995), thought to be carbonatites. However, M.S. Garson (pers. comm., 1990) says that they are not carbonatites.