Chapter 15: Lakes of the Gregory Rift Valley: Baringo, Bogoria, Nakuru, Elmenteita, Magadi, Manyara and Eyasi

Abstract

The lakes of the Gregory Rift Valley are protected in national parks, reserves and conservation areas. Many of the lakes occur in areas of spectacular landforms located at the base of prominent escarpments. Palaeo-lakes were on average far larger (and deeper) during the Pleistocene. Currently, lakes are mostly relatively small, finger-shaped bodies with a maximum length of a few tens of kilometres. Lake basins have limited catchment and few outlets; rift platforms are tilted outwards so that major rivers flow away from the rift valley. Evaporation exceeds inflow resulting in high levels of alkalinity and salinity. The high sodium content is enhanced due to erosion of the sodium-rich volcanic rocks that characterise the Gregory Rift Valley. Lakes Bogoria, Nakuru, Elmenteita, Manyara and Eyasi are typical in this regard: they are finger-shaped, extremely shallow and markedly alkaline. They have an average pH of 10. Lakes Magadi and Natron are extraordinarily toxic; they contain brines with a pH of 12 that fossilises trees and animals by replacing the wood or bones with sodium carbonate. The alkaline lakes include salt deposits which are a mixture of two naturally occurring compounds of sodium carbonate, trona and natron. The salt deposits of Lake Magadi are quarried for soda ash. Lakes Baringo and Naivasha differ from the alkaline lakes in that they have a more rounded form, occur in basins with larger catchments and are dominated by freshwater. Important vertebrate and hominin fossils have been discovered in the Miocene–Pleistocene sediments of the Tugen Hills, near Lake Baringo. Geysers and hot springs discharge sulphurous brines into some lakes, including Baringo and Manyara. The geysers associated with Lake Bogoria are particularly well known. Many lakes and foreshores sustain significant concentrations of wildlife and they are refuges for more than 400 species of birds. Huge concentrations of flamingoes occur on some of the alkaline lakes.