Turkana - Lake Turkana
The Lake
Life in the desert lake
The Omo River Delta
|
||
|
Turkana - Lake Turkana |
|
| See also Lake Turkana - Mankind's Origins. |
||
| In this page: The Lake Life in the desert lake The Omo River Delta |
||
By its very existence, the windswept expanse of Lake Turkana is something of a miraculous anomaly. Situated in the arid lands of northwestern Kenya, it is the largest permanent desert lake in the world. Roughly 250km long and 40-60km wide, it occupies a clearly delineated trough in the Northern Rift Valley, lying mainly in Kenya but with its marshy northern end - the Omo River Delta - jutting into Ethiopia. To the west of the delta, the 'Ilimi Triangle' officially lies in Sudan but is administered by Kenya, and is where Sudan, Ethiopia and Kenya meet.
The climate is harsh, with a mean annual rainfall of under 250mm and a merciless hot wind which blows almost constantly from the southeast, where the great hulk of Mount Kulal - a UNESCO International Biosphere Reserve since 1978 - rises to 2164 metres above sea level from the lake's level of around 370 metres.
The lake has no outlet, and is gradually receding due to a combination of intense evaporation and lower rainfall. Its depth averages around 30-35 metres, and at its deepest reaches just over 100 metres. But in the geologically recent past (some 9000 years ago), the lake level was over a hundred metres higher and was connected to the White Nile by means of an outlet through the Lotikipi plain beyond Lokitaung and the Murua Rithi Hills, to the northwest. In the much more distant past, two million years ago, the lake stretched at least 160km further south and included Lake Baringo. Earth movements at the end of the Pleistocene Epoch (possibly 10,000 years ago) separated the two lakes, and volcanic activity cut-off the outlet to the Nile.
Nowhere in the Rift valley are the violent cataclysms that formed it more apparent than around the shores of Lake Turkana. To the south and east, the beaches consist of a coarse black sand, which comes from jagged lava flows which stretch off into the rocky hinterland. The landscape here is unremittingly severe, where only the hardiest acacia, some tussocks of thorny grass and - of course - the Turkana, can survive. Further north, the aspect softens somewhat, where the rocky ledge has been undercut by past movements of the lake; here, stands of reeds attract a surprising number of animals, including zebra, oryx, lion, hartebeest and waterbuck.
On the southern shore, the extinct volcanic cones of Abili Agituk and Naboyatom (or Nabouyotum; "Stomach of Elephant") jut out into the water, and form the extremity of the volcanic "Barrier" which plugs the lake's southern end, beyond which lies Kenya's hottest and least hospitable place, the Suguta Valley.
The lake's three islands - rather prosaically named North, Central and South - are also of volcanic origin, most obviously Central island with its three perfectly formed crater lakes. As a result of run-off from the lava flows, the lake's waters are mildly alkaline, enough to give the water a slightly slimy, soapy feel, but not so much as to prevent life, as fresh water from Ethiopia's Omo River - the lake's only perennially-flowing inlet - dilutes the waters.
The western shores are lower that those on the east, and consist mainly of sand dunes, sand spits, and mudflats. This is where the lake's constantly fluctuating level is most apparent: for example, the six metre fall in the lake's level between the 1960s and late-1990s left the former shoreside village of Kalokol almost 8km from the waters. Equally dramatic was the subsequent four metre rise after the unusually high 1997-98 El Niño rains, which brought the waters back to within 3km of the village. However, perhaps due to the effect of such repeated flooding, the overly alkaline soil on the western shore is largely sterile, except where a rare fresh-water spring wells up and produces an oasis of doum palms, as it does at Eliye Springs.
Despite the barren surroundings, the lake itself is a surprisingly rich if somewhat limited habitat for life, which on the lowest level manifests itself in an immense bloom of soda-loving algae, which can change the colour of lake from sky blue to jade green, according to the effects of wind and sunlight. The algae, in turn, support large numbers of fish, especially the enormous Nile perch, tigerfish, bichir, and various species of tilapia.
Feeding on them is the world's largest population of Nile crocodiles, of which some 12,000 were estimated to be breeding on Central Island in 1981; there are no recent figures available. The crocodiles have remained almost unchanged for 130 million years, and breed mainly on the flat and seldom-visited shores of two of the three water-filled craters of Central island, one of which is connected to the lake. Whilst it is now illegal to hunt them, many are caught in the fishermen's nets, and they were traditionally hunted by the El Molo on the eastern side of the lake, and occasionally by Turkana. The meat is considered a delicacy, but the skins, which are soft as a result of the lake's alkaline waters and have horny nodules on the belly, have no commercial value. The crocodiles are generally very timid, although those in the Omo Delta have a reputation for ferocity, perhaps because the Merille who live there do not hunt them.
Other lake fauna includes hippo, and a plethora of birds, many of them migratory. Of the 350 species recorded on or around the lake, only few live here all year round; these include flamingos, cormorants and kingfishers.
Over on the northeastern shore, Sibiloi National Park - close to the Koobi Fora archaeological site at Alia Bay - is one of Kenya's remotest parks, and protects a surprising variety of wildlife, including zebra, ostrich, gazelle, gerenuk, hartebeest, oryx and a unique sub-race of topi called the Tiang (Damaliscus lunatus). There are apparently lions and cheetah, and until the start of twentieth century, vast herds of elephant, too, as the explorer Sámuel Teleki related in his diary:
After several days, always in fear of hunger and thirst, we marched through a district where large herds of elephants lived. Several fell victim to our guns. Three we had wounded sought refuge in the lake, but by morning only one remained. So the Count sent three men out in our canvas boat. They were either to shoot the animal, or to drive him ashore. The boat circled the quarry, but the elephant did not budge an inch, no matter how many bullets struck his body. Suddenly, he charged furiously, and the men jumped overboard. In the twinkling of an eye he was upon the fragile craft, which he seized with his trunk. He shook it, crushed it, tossed it about, and then contemptuously flung it aside. Finally, he marched with slow and stately steps through the water and disappeared behind a peninsula in the shoreline.
The elephant herds are now all but gone, partly because of the ever drier climate, but mainly thanks to the actions of European hunters throughout the colonial period, of which the most callous was without question the deeply dislikable Lord Delamere (who was the primary beneficiary of the expulsion of the Maasai from the Rift Valley), who in 1897 took six tons of ivory from Lake Turkana.
A stark reminder of the dryness which currently envelops the lakeshore is the petrified forest of Sibiloi, which has been a UNESCO World Heritage Site since 1997.
The Omo River is Turkana's only perennial tributary, providing the lake with 80-90% of its intake. Until the 1950s, its waters were relatively clean, but ever since agriculture and erosion of topsoil caused by land clearance and deforestation in Ethiopia has led to the river dumping vast amounts of sediment into the lake.
As the river's silt-laden water is nevertheless lighter than the soda-dense waters of the lake, it 'floats' on top of the lake for many kilometres before the waters mix. A unusual result of this is that as the river current gradually slows down, allowing silt and topsoil to sink to the lake bed and form firm ground, the river continues to flow above it, giving the impression not that the delta has been gouged out of silt, but that the various branches of the river are carried far into the lake on the tops of levees or canals with raised banks.
As the lake has no outlet, water is lost mainly by evaporation, which has been estimated at an incredible 2.34 metres per year. But as the influx is primarily the River Omo, the lake's level is subject to wild fluctuations during periods of heavy rain or drought in the Ethiopian Highlands. In general, however, it appears that East Africa is becoming drier over the centuries, and in consequence the lake's level is tending to fall.
These images of the Omo Delta, taken in 1973, 1989 and 1995 by various Landsat satellites, vividly show the progressive siltation of the Omo Delta coupled with the effects of the falling water level. All are courtesy of the USGS EROS Data Center. Click on the images for larger versions.
 |
 |
 |
 |
|
