The southern end of the Gregory Rift Valley terminates against the craton. The volcanic area of this rift covers the surface interface between the Mozambique orogenic fold belt and the Tanzania Craton. A superplume exists beneath the craton. An indirect effect of rift and plume associated volcanism in the Tanzania Craton is the high levels of soil nutrients in Serengeti provided by volcanic ash from Ol Doinyo Lengai.