Late Quaternary Shorelines of Lake Naivasha, Kenya

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Abstract
Dr. Celia Kamau is on the staff of Kenyatta University College, Nairobi. She has carried out exhaustive research on the lake basins of the central Rift Valley, much of it in association with archaeologists. The Lake Naivasha basin in the Kenya Rift Valley contains evidence that the lake has formerly stood well above its 1972 level of about 1890 m. This evidence was located and levelling was undertaken to determine the elevation of the former high lake shoreline or shorelines. A possible beach ridge was located at an elevation of 2006–2008 m, and beach gravels of obsidian, lava and pumice occurred at many localities up to a maximum of 1990–1996 m. It may tentatively be concluded that the lake rose to a maximum level of 2000±10 m. No conclusive proof of a lower shoreline level could be found. At present a rising lake in this basin would flow southwards down the Njorowa Gorge when it reached an elevation of 1940–1950 m: lowering of the terrain in this area has clearly taken place since the time of the 2000-m lake. The possible sequence of events during the formation of this gorge is outlined, involving the process of ‘foundation scouring’. It is concluded that during the period under study, Lake Naivasha did not flow northwards over the pass at Gilgil into the Nakuru-Elmenteita basin. No direct evidence of the age of the 2000-m lake was found during the present study. Correlation with dates from the Nakuru-Elmenteita basin and from cores taken from beneath Lake Naivasha indicate that it may be of the order of 10,000 years old. A search for archaeological material in the basin was generally unfruitful. Though many surface concentrations of worked obsidian were found, no discrete sites were located.