Being located in eastern Africa, the rift valley is not far. The full name is East African Rift System (EARS). There are two convection cells below Africa, and at the border the mantle flows up and diverges, pulling the two sides away from each other. The result will be that an ocean opens and two separate plates or continents will move away from each other. The current events are, a graben structure, because the sides move away, cracks open and the material in the middle falls down into the crack. At the same time magma from below uses the cracks to move up and cause volcanism.
The western two-thirds of the country consists of Precambrian basement rocks which forms the African craton. Very old rocks, folded numerous times, heated and under pressure, transformed into metamorphic rocks, Mostly insoluble and hard, gneiss and shist. And on top the much younger Pliocene–Pleistocene volcanism, creating huge volcanoes like Mount Kenya or Kilimanjaro on the border to Tanzania.
The southeast corner of the country is formed by much younger rocks than the craton. It consists of sediments of the Karoo System of Permian to Late Triassic age and a strip of Jurassic age sediments along the coast in the Mombasa area. The Anza trough is a NW–SE trending Jurassic rift, which extends from the Indian Ocean coast to the Sudan northwest of Lake Turkana. The Anza Rift was formed by the break–up of Gondwana.
Kenya is one of the few countries in which karst cavities are scarce while volcanic caves are rather abundant and widespread throughout the whole country. The great variability in lava composition caused the formation of quite different cavities. Several lava tubes are on the list of the longest lava tubes of the world. The 8th International Symposium on Volcanospeleology was held in Nairobi in February 1998.