The Menengai volcano is composed almost entirely of strongly peralkaline, Si-oversatured trachytes. No mafic or intermediate products have yet been identified. The volcano has had a complex geochemical evolution, resulting from the interplay of magma mixing, crystal fractionation and liquid state differentiation. The controlling mechanism at any time was related to the growth stage of the complex, the presence of volatile gradients in the chamber, and the distribution of magma densities in the chamber. Prior to a major ash flow eruption, the magma reservoir was growing by the addition and mixing of two or more trachytic melts, only slightly different in composition. A volatile-rich cap eventually separated from the lava-forming zone and became compositionally zoned by liquid state processes.