SEA LEVEL CHANGES ON THE KENYAN COAST DURING THE QUATERNARY PERIOD

Kenya is found on the African continent in the East bordering the Western Indian Ocean. The Kenya coast is approximately 600 km long from Kiunga in the north to Vanga in the south. Along the coast of Kenya, coastal terraces, dunes, cliffs and beach ridges are among the most important geomorphological features indicative of the Quaternary sea level changes. Coral reefs in coastal Kenya occur as fringing coral platforms, running parallel to the shoreline on the coastline. In other places the coral reefs occur as platforms on the intertidal flat and as backshore raised reef limestone, forming cliffs of 12- 15 m high.

In Northern Kenya dune ridges are the main characteristics of the coast. Sometimes at least two generations of dune ridges can be found, the older probably being of young Pleistocene age, the younger closer to the sea of Holocene age.

In the Southern Kenya, the coast becomes very complex. Cliffs formed by wave erosion in coral rocks with raised shorelines are the most prominent feature indicating a shoreline of emergence. However, where fresh water reaches the coast, deep creeks are found. Mangrove swamps are very common especially in muddy areas where fresh water enters the coast.

Coastal terraces occur as distinctive platforms in stepwise manner in many places along the coast of Kenya. The terraces were cut during the Pleistocene to recent fluctuations in sea level. The beach ridges, closely associated with the dunes are of variable Holocene age. Coastal terraces that have been recognized by various workers are the Matuga surface (90-140 m), Changamwe terrace (45-70 m), Ganda terrace (20-37 m), Kilifi terrace (15-18 m), Malindi terrace (7-10 m), Shelly beach terrace (4-5 m), Leven Reef terrace (0-2 m) and the submarine platforms at -5 and -15 m below datum.

It has been assumed that the shore terraces of Kenya correspond to eustatic movements of sea level. However, if the dating were reasonably correct, the terraces would be found well below sea level if no rise of land had occurred during the time in question. Evidence of tectonic movements can be seen in the dipping of sedimentary strata on the coast in Kenya. It can therefore be concluded that the geomorphology of the Kenya coast is not only as a result of sea level changes but also due to isostatic readjustments and tectonic movements.