F.M.Omondi 

2008

 

The great rift valley Lakes 

[P ]  

THE RIFT VALLEY LAKES

In Gamblian times (Upper Pleistocene) Lakes Naivasha, Elmenteita, and Nakuru were all connected. It is also thought that Lakes Baringo and Turkana were formerly part of one lake. It is certain that since Upper Pleistocene times the lakes have gradually dwindled owing to more arid conditions and at present there is a chain of seven lakes in the Kenya section of the Rift Valley, all very shallow with the exception of Lake Turkana. We will now look briefly at each of them in turn and see a little about their past histories and methods of formation.

1. Lake Baringo

• Coordinates 0°38′N 36°05′E

0°38′N 36°05′E

• Primary inflows El Molo, Ol Arabel

• Surface area 130 km²

• Surface elevation 1000 m (3200 ft) Lake Baringo is, after Lake Turkana, the most northern of the Great Rift Valley lakes of Kenya, with a surface area of about 130 km² and an elevation of about 970 m. The lake is fed by several rivers, El Molo, Perkerra and Ol Arabel, and has no obvious outlet; the waters are assumed to seep through lake sediments into the faulted volcanic bedrock. It is one of the two freshwater lakes in the Rift Valley in Kenya, the other being Naivasha. It lies off the beaten track in a hot and dusty setting and over 470 species of birds have been recorded there, occasionally including migrating flamingos. A Goliath Heronry is located on a rocky islet in the lake known as Gibraltar. The lake is part of the Great Rift Valley system. The Tugen Hills, an uplifted fault block of volcanic and metamorphic rocks, lies west of the lake. The Laikipia Escarpment lies to the east. Water flows into the lake from the Mau Hills and Tugen Hills. It is a critical habitat and refuge for more than 500 species of birds and fauna, some of the migratory waterbird species being significant regionally and globally. The lake also provides an invaluable habitat for seven fresh water fish species. One, Oreochromis alcalicus baringoensi, is endemic to the lake. Lake fishing is important to local social and economic development. Additionally the area is a habitat for many species of animals including the hippopotamus (Hippopotamus amphibious), crocodile (Crocodylus niloticus) and many other mammals, amphibians, reptiles and the invertebrate communities Fish stocks in the lake are now low and water levels have been reduced by droughts and over-irrigation. The lake is commonly turbid with sediment, partly due to intense soil erosion in the catchment, especially on the Loboi Plain south of the lake. The lake has several small islands, the largest being Ol Kokwe Island. Ol Kokwe, an extinct volcanic centre related to Korosi volcano north of the lake, has several hot springs and fumaroles, some of which have precipitated sulphur deposits. A group of hot springs discharge along the shoreline at Soro near the northeastern corner of the island. Several important archaeological and palaeontological sites, some of which have yielded fossil hominoids and hominins, are present in the Miocene to Pleistocene sedimentary sequences of the Tugen Hills.

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THE RIFT VALLEY LAKES

The main town near the lake is Marigat, while smaller settlements include Kampi ya Samaki and Loruk. The area is increasingly visited by tourists and is situated at the southern end of a region of Kenya inhabited largely by pastoralist ethnic groups including Il Chamus, Rendille, Turkana and Kalenjin. Lake Baringo is about 20 Kilometers long and 8.9 Kilometers wide, with an almost uniform depth of 7 metets; it lies at an altitude of 976 meters. Although it is so small, its waters are quite fresh (unlike the other small lakes in the Rift Valley, which are extremely alkaline). In spite of this it has no visible outlet; Professor Gregory explained the freshness of the water by assuming seepage into the lavas to the north of the lake. Old lake terraces are to be seen at 9 meters and 5 meters above present level, and Lake Baringo is thought to have been connected formerly with Lake Turkana via the Sugota river and hence with the Nile, as the lake beds contain fresh-water shells of Nilotic type which are not living in the lake to-day. The lake is bounded by fault scarps and Kamasian deposits are exposed both to the west and east of the lake, the latter deposits taking the form of torrential gravels. In 1931 Dr. Worthington noted that the lake had risen considerably in recent years, but apart from minor fluctuations, it is becoming gradually shallower and the southern end is silting up. It contains one large and several small volcanic Islands, the eroded remains of volcanic plugs; on the shores of the largest Island are a number of boiling sulphurous springs.

English: Lake Baringo of the Great Rift Valley, Kenya. August, 199

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2. Lake Bogoria (HANNINGTON)

• Coordinates 0°15′N 36°06′E 0°15′N 36°06′E

• Lake type saline, alkaline, meromictic

• Primary inflows

Sandai and Emsos rivers, springs

• Catchment area 700 km² • Max. length 34 km • Max. width 3.5 km • Surface

elevation 990 m

Lake Bogoria is a saline, alkaline lake that lies in a volcanic region in a half-graben basin south of Lake Baringo, Kenya, a little north of the equator. Lake Bogoria, like Lake Nakuru, Lake Elmenteita, and Lake Magadi further south in the Rift Valley, and Lake Logipi to the north, is home at times to one of the world's largest populations of lesser flamingoes. The lake is a Ramsar site and has been protected National Reserve since November 29, 1973. Lake Bogoria is shallow (about 10 m depth), and is about 34 km long by 3.5 km wide, with a drainage basin of 700 km². Local features include the Kesubo Swamp to the north and the Siracho Escarpment to the east, both within the National Reserve. The reserve is also famous for its geysers and hot springs. The lake waters are of Na-HCO3-CO3 composition. They originate from inflow from the Sandai and Emsos rivers, and from about 200 alkaline hot springs that are present at three onshore sites: Loburu, Chemurkeu, and a southern group (Ng'wasis, Koibobei, Losaramat). Other springs discharge directly from the lake floor. Lake Bogoria also contains the highest concentration of true geysers in Africa (at least 18 are known). The lake waters are alkaline (pH: 10.5) and saline (up to 100 g/L Total Dissolved Salts). The lake has no surface outlet so the water becomes saline mainly through evaporation, which is high in this semi-arid region. The lake itself is meromictic (stratified) with less dense surface waters lying on a denser more saline bottom waters. Although hypersaline, the lake is highly productive with abundant cyanobacteria (Arthrospira fusiformis) that feed the flamingoes, but few other organisms inhabit the lake. The lake has not always been saline. Sediment cores from the lake floor have shown that freshwater conditions existed for several periods during the past 10,000 years, and that lake level was up to about 9 m higher than its present level of about 990 m above sea-level. At times it might have overflowed northward towards Lake Baringo. At times, during the late Pleistocene it might have been united with a larger precursor of modern Lake Baringo, but this is still uncertain. The lake area was the traditional home of the Endorois people, who were forced to leave the area in the 1970s and are now challenging their removal at the African Commission on Human and Peoples' Rights. Lake Bogoria is about 16 Kilometers long and less than 5 Kilometers wide. It lies about 31 meters higher than Lake Baringo, to which it was probably connected in Middle Pleistocene times.

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THE RIFT VALLEY LAKES

Its waters are very shallow and have a high alkaline content. On the western side are many hot springs, some in the water and some on the edge of the lake, and one of them is an intermittent geyser. The springs are of various temperatures, some being boiling and others so cold that cattle are able to drink at them. Some of the springs in the lake itself throw up mud. Tree stumps can be seen near the lake which is covered with a layer of lime 20 millimeters thick, showing that the lake must have stood about 5meters higher in recent times, so recent that the wood inside the stumps is still fibrous. The natives say that twenty-five generations ago the lake rose very rapidly and drowned many people.

The image shows flamingos nesting on the shoreline of Lake Bogoria in Kenya. Photo made by Bob Walker in Kenya, Africa in 1988.

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3. Lake Elmenteita

• Coordinates 0°27′S 36°15′E 0°27′S 36°15′E

• Basin countries Kenya • Surface area 18 km² • Surface elevation 1,670 meters ASL

Lake Elmenteita, also spelled Elementaita, is a soda lake, in the eastern limb of East Africa's Great Rift Valley, about 120 km northwest of Nairobi, Kenya Elmenteita is derived from the Masaai word muteita, meaning "dust place", a reference to the dry and dusty quality of the area, especially between January and March. The town of Gilgil is located near the lake. In the south-to-north sequence of Rift Valley lakes, Elmenteita is located between Lake Naivasha and Lake Nakuru. The major Nairobi—Nakuru highway runs along the nearby escarpment affording motorists a spectacular vista towards the lake. The Lake Elmenteita area saw its first white settlement when Lord Delamere (1879-1931) established his Soysambu, a 100,000-acre (400 km²) ranch, on the western side of the lake. Delamere gifted the land nearest the lake to his brother-in-law, the Honorable Galbraith Lowry Egerton Cole (1881-1929), part of whose "Kekopey Ranch", where he is buried, is preserved today as the Lake Elementaita Lodge. The nearby Soysambu Farm is still occupied by Lord Delamere's descendants, including the controversial Thomas P. G. Cholmondeley. Lake Elmenteita has been a Ramsar site since 2005. Over 400 bird species have been recorded in the Lake Nakuru/Lake Elmenteita basin. Elmenteita attracts visiting flamingoes, both the Greater and Lesser varieties, which feed on the lake's crustacean and insect larvae and on its suspended blue-green algae, respectively. Tilapia were introduced to the lake from Lake Magadi in 1962 and since that time the flamingo population has dwindled considerably. The tilapia attracts many fish-eating birds that also feed upon the flamingo eggs and chicks. Over a million birds that formerly bred at Elmenteita are now said to have sought refuge at Lake Natron in Tanzania. The lake's shores are grazed by zebra, gazelle, eland and families of warthog. The lake is normally very shallow (< 1 m deep) and bordered by trona-encrusted mudflats during the dry seasons. During the late Pleistocene and early Holocene, Lake Elmenteita was at times united with and expanded Lake Nakuru, forming a much larger dilute lake. Remnants of the former joined lake are preserved as sediments at various locations around the lake basins, including former shorelines. This small lake is about 15 meters higher than Lake Nakuru and its deepest part is only 1.91 meters. It too is full of soda salts, so that the only life it can support consists of rotifers, algre, and diatoms (all microscopic organisms). These form the diet of the huge flocks of flamingos which are nearly always to be seen there, though periodically they migrate to Lake Bogoria. Both Bogoria and Elmenteita contain several hot springs-possibly these have an influence on the growth of the organisms on which the flamingos feed. The Kariandusi and Mereroni streams enter the lake; they both derive their waters from

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THE RIFT VALLEY LAKES

hot springs and so never dry up.

Lake Elementaita from the Nairobi-Nakuru highwayDec 2001

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THE RIFT VALLEY LAKES

Lake Elementaita from the Nairobi-Nakuru highwayDec 2001

4. Lake Logipi

• Coordinates 2°14′N 36°34′E 2°14′N 36°34′E

• Primary inflows hot springs • Basin countries Kenya • Max. length 6 km • Max. width 3 km • Max. depth 3-5 m

Lake Logipi is a saline, alkaline lake that lies at the northern end of the arid Suguta Valley in the northern Kenya Rift. It is separated from Lake Turkana by the Barrier volcanic complex, a group of young volcanoes that last erupted during the late 19th Century or early 20th Century. Saline hot springs discharge on the northern shoreline of Lake Logipi and at Cathedral Rocks near its southern limit, and help to maintain water at times of extreme aridity. During the rainy season, the lake is also recharged from the Suguta River which flows northward along the Suguta Valley, periodically forming a temporary lake (Lake Alablab) that unites with Logipi. Lake Logipi has a maximum depth of 3 to 5 m, and is about 6 km wide by 3 km long. Its waters are of sodium bicarbonate composition with a pH of 9.5-10.5 and salinity (total

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THE RIFT VALLEY LAKES

dissolved salts) that varies from < 20 g/l to > 50 g/l. Efflorescent salt crusts (trona) are present around its margins. Flamingoes frequently inhabit the saline waters feeding on cyanobacteria (Arthrospira spp. - formerly termed Spirulina) and other plankton.

5. Lake Magadi • Location Rift Valley

• Coordinates 1°52′S 36°16′E 1°52′S 36°16′E

• Basin countries Kenya • Surface area 100 km²

Lake Magadi is the southermost lake in the Kenyan Rift Valley, lying in a catchment of faulted volcanic rocks, north east of Lake Natron. During the dry season, it is 80% covered by soda and is well known for its wading birds, including flamingos. Lake Magadi is a saline, alkaline lake, approximately 100 square kilometers in size, that lies in a graben. The lake is an example of a "saline pan". The lake water, which is dense sodium carbonate brine, precipitates vast quantities of the mineral called trona (sodium sesquicarbonate). In places, the salt is up to 40 m thick. The lake is recharged mainly by saline hot springs (temperatures up to 86°C) that discharge into alkaline "lagoons" around the lake margins, there being little surface runoff in this arid region. Most hot springs lie along the northwestern and southern shorelines of the lake. During the rainy season a thin (<1 m) layer of brine covers much of the saline pan, but this evaporates rapidly leaving a vast expanse of white salt that cracks to produce large polygons. A single species of fish, a cichlid called Alcolapia grahami, inhabits the hot, highly alkaline waters of this lake basin and is commonly seen in some of the hot spring pools around the shoreline where the water temperature is less than 45°C. Lake Magadi was not always so saline. Several thousand years ago (during the late Pleistocene to mid-Holocene) the Magadi basin held a freshwater lake with many fish, whose remains are preserved in the High Magadi Beds, a series of lacustrine and volcaniclastic sediments preserved in various locations around the present shoreline. Evidence also exists for several older Pleistocene precursor lakes that were much larger than present Lake Magadi. At times, Lake Magadi and Lake Natron were united as a single larger lake. Magadi township lies on the lake's east shore, and is home to the Magadi Soda factory, owned by Tata India since December 2005. This factory produces soda ash, which has a range of industrial uses. From Lake Naivasha the floor of the Rift Valley descends gradually until it is only 610 meters at Magadi. This lake is famous for its deposits of trona (sesquicarbonate of soda) and forms the largest natural source of soda in the world. It is being renewed, probably by alkaline waters which have a deep-seated origin, at a rate faster than it is being removed, so the supply seems practically inexhaustible. At the present time, the I.C.I. are turning out 100,000 tons of trona a year and as there is a world shortage of this salt, still more could be produced with advantage if the necessary rolling stock were available to transport it.

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Lake Madagi, Kenya, R. Renaut: original photograph2005-11-13

6. Lake Naivasha • Coordinates 0°46′6.70″S, 36°21′2.32″E

0°46′6.70″S, 36°21′2.32″E

• Basin countries Kenya • Surface area 139 km² • Average depth 6 m (20 ft) • Max. depth 30 m (100 ft) • Surface elevation 1,884 m (6,180 ft)

Lake Naivasha is a freshwater lake in Kenya, lying North West of Nairobi, outside the town of Naivasha. It is part of the Great Rift Valley. The name derives from the local Maasai name Nai'posha, meaning "rough water" because of the sudden storms which can arise. The lake has a surface area of 139 km², and is surrounded by a swamp which covers an area of 64 square km, but this can vary largely depending on rainfall. It is situated at an altitude of 1,884 metres (6,180 feet). The lake has an average depth of 6 m (20 feet), with the deepest area being at Crescent Island, at a maximum depth of 30 m (100 ft). Njorowa Gorge used to form the lake's outlet, but it is now high above the lake and forms the entrance to Hell's Gate National Park. The lake is home to a variety of wildlife; over 400 different species of bird have been reported. There is a sizeable population of hippos in the lake. There are two smaller lakes in the vicinity of Lake Naivasha: Lake Oloiden and Lake Sonachi (a green crater lake). The Crater Lake Game Sanctuary lies nearby, while the lake shore is known for its population of European immigrants and settlers.

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Between 1937 and 1950 the lake was used as a landing place for flying boats on the Imperial Airways passenger and mail route from Southampton in Britain to South Africa. It linked Kisumu and Nairobi. Joy Adamson, the author of Born Free, lived on the shores of the lake in the mid-1960s. Also on the shores of the lake is the Djinn Palace, which gained notoriety in the Happy Valley days between the two world wars. It now forms part of the Oserian flower farm. Floriculture forms the main industry around the lake. However, the largely unregulated use of lake water for irrigation is reducing the level of the lake and is the subject of concern in Kenya. Fishing in the lake is also another source of employment and income for the local population. The lake varies in level greatly and almost dried up entirely in the 1890s. Having refilled, water levels are now dropping again. The town of Naivasha (formerly East Nakuru) lies on the north east edge of the lake. In 1981, the first geothermal plant for Lake Naivasha was commissioned and by 1985, a total of 45 MW of electricity was being generated in the area. The water level for Lake Naivasha reached a low level of 0.6 m depth in 1945, but the water level rose again, with minor drops, to reach a maximum depth nearly 6 m in 1968. There was another major decline of the water level in 1987, when the depth reached 225 cm above the lake bottom. The decline of the lake water level in 1987 increased concern in the future of geothermal industry, and it was speculated that Lake Naivasha underground water might be feeding the geothermal reservoir at Olkaria. Hence, the decline in the lake water would affect the future of the geothermal industry. Lake Naivasha lies at the highest point of the Rift Valley, 1890 meters. Its average depth in 1929 was 10.4 meters, but one hole near the concave side of Crescent Island was found to be 18.3 meters. Crescent Island and two other small islands are part of the submerged rim of a volcano, whose crater forms the deepest part of the lake. Since 1929 regular observations have been made of the fluctuation of the lake whose level, in common with the other Rift Valley lakes, is found to be sinking fairly rapidly (it dropped 9.144 meters between 1929 and 1940). Lake Naivasha has no visible outlet nowadays, though in Gamblian times it overflowed through the Njorowa Gorge (Hells gates). In spite of this its waters are quite fresh and fish are able to live in it. The explanation used to be that the lake must have a subterranean outlet, but the modern view is that river capture took place in the upper Melawa, resulting in a much greater flow of fresh water into the lake. Before this happened the level of the lake was probably lower and its soda content higher, as at this time the large trees seen standing in the lake to-day must have been on dry land. The present basin dates from the faulting and volcanic activity of the Middle Pleistocene period. Before this, as we have seen, the Rift Valley lakes did not exist but instead the whole of this area was covered by Lake Kamasia. Kamasian beds are exposed near the lake in the Njorowa Gorge, beneath a covering of comendite lava and volcanic ash. The gorge must have been eroded by a great river through the Kamasian deposits: it is about 19 Kilometers long and a number of high-pressure steam-jets can be seen issuing from its' sides, which have been exposed at depth by erosion. "Fischer's Tower," composed of lava, has been left standing near the entrance to the gorge(Hell’s gate), while farther down is a similar pinnacle known as "EI Barta" (Maasai: the horse). Along the sides of

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THE RIFT VALLEY LAKES

the gorge are fourteen prehistoric obsidian mines-the obsidian or volcanic glass was used extensively by Stone Age man for making his tools. In the Melawa Gorge, east of Lake Naivasha, Gamblian beds are exposed which show evidence that this pluvial period had three maxima. A Makalian terrace has also been left at 31 meters above 1929 lake level, in this same gorge, while a Nakuran terrace can be seen at 15 meters. Besides the Melawa, the Little Gilgil River flows into the lake and along its banks near the main Nairobi-Nakuru road more Gamblian deposits are exposed.

Red-knobbed Coots at Lake NaivashaOctober 08, 2006 at 15:18

7. Lake Nakuru Lake Nakuru is one of the Rift Valley soda lakes. It lies to the south of Nakuru, in central Kenya and is protected by a small Lake Nakuru National Park.

Flamingo are feeding at Lake Nakuru, Kenya; Greater and Lesser Flamingos flock to the lake.

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THE RIFT VALLEY LAKES

The lake's abundance of algae attracts the vast quantity of flamingos that famously lines the shore. Other birds also flourish in the area, as do warthogs, baboons and other large mammals. Black and White rhinos have also been introduced. The lake's level dropped dramatically in the early 1990s but has since largely recovered. Nakuru means "Dust or Dusty Place" in Maasai language. Lake Nakuru National Park, close to Nakuru town, was established in 1961. It started off small, only encompassing the famous lake and the surrounding mountainous vicinity. Now it has been extended to include a large part of the savannahs. Lake Nakuru is 13 Kilometers long, 6.5 Kilometers wide, and stands at an altitude of 1760 meters. Its greatest depth was found to be only 2.79 meters (1929) and this is uniform except at the edges. On the whole it is receding fairly rapidly and it dried up completely in 1939-40, but since then it has been gradually filling up again. Its waters are rich in soda salts which blow in an unpleasant white cloud for Kilometers around when there is a strong wind. The lake is fed by three streams, the Njoro, Makalia, and Nderit, but the last two of these are often dry.

Uizicht over Lake Nakuru. Foto gemaakt door mij in Mei 2003.

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8. Lake Turkana Lake Turkana formerly known as Lake Rudolf is a lake in the Great Rift Valley in Kenya, with its far northern end crossing into Ethiopia. It is the world's largest permanent desert lake and the world's largest alkaline lake. By volume it is the world's fourth largest salt lake after the Caspian Sea, Lake Issyk-Kul and the (shrinking) Aral Sea, and among all lakes it ranks twentieth. The water is potable but not palatable. It supports a rich lacustrine wildlife. The climate is hot and very dry. The rocks of the surrounding area are predominantly volcanic. Central Island is an active volcano, emitting vapors. Outcrops and rocky shores are found on the East and South shores of the lake, while dunes, spits and flats are on the West and North, at a lower elevation.

Lake Turkana seen from the South Island. On-shore and off-shore winds can be extremely strong as the lake warms and cools more slowly than the land. Sudden, violent storms are frequent. Three rivers (the Omo, Turkwel and Kerio) flow into the lake, but lacking outflow its only water loss is by evaporation. Lake volume and dimensions are variable. For example, its level fell by 10 meters between 1975 and 1993. Due to temperature, aridity and geographic inaccessibility, the lake retains its wild character. Nile crocodiles are found in great abundance on the flats. The rocky shores are home to scorpions and carpet vipers. Although the lake and its environs have been popular for expeditions of every sort under the tutelage of guides, rangers and experienced persons, they certainly must be considered hazardous for unguided tourists. Lake Turkana National Parks are now listed as a UNESCO World Heritage Site. Sibiloi National Park lies on the lake's eastern shore, while Central Island National Park and South Island National Park lie in the lake. Both are known for their crocodiles. Lake Turkana is an East African Rift feature. A rift is a weak place in the Earth's crust due to the separation of two tectonic plates, often accompanied by a graben, or trough, in which lake water can collect. The rift began when East Africa, impelled by currents in the mantle began separating from the rest of Africa, moving to the northeast. Currently the graben is 320 km wide in the north of the lake, 170 km in the south. This rift is one of two, and is called the Great or Eastern Rift. There is another to the west, the Western Rift. The basement rocks of the region have been dated by two analytical determinations to 522 and 510 million years ago. No rift was in the offing at that time. A rift is signalled by volcanic activity through the weakened crust. The oldest volcanic activity of the region

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occurred in the Nabwal Hills northeast of Turkana and is dated to 34.8 million years ago in the late Eocene. The visible tectonic features of the region result from extensive extrusions of basalt over the Turkana-Omo basin in the window 4.18-3.99 million years ago .These are called the Gombe Group Basalts. They are subdivided into the Mursi Basalts and the Gombi Basalts. The two latter basalts are identified as the outcrops that are the rocky mountains and badlands around the lake. In the Omo portion of the basin, of the Mursi Basalts, the Mursi Formation is on the west side of the Omo, the Nkalabong on the Omo, and the Usno and Shungura east of the Omo. Probably the best known of the formations are the Koobi Fora on the east side of Turkana and the Nachukui on the west. Short-term fluctuations in lake level combined with periodic volcanic ash spewings over the region have resulted in a fortuitous layering of the ground cover over the basal rocks. These horizons can be dated more precisely by chemical analysis of the tuff. As this region is believed to have been an evolutionary nest of Hominins, the dates are important for generating a diachronic array of fossils, both Hominoid and non-Hominoid. Many thousands have been excavated. Terraces representing ancient shores are visible in the Turkana basin. The highest is 75 m above the surface of the lake (only approximate, as the lake level fluctuates), which was current about 9500 years ago, at the end of the Pleistocene. It is generally theorized that Turkana was part of the upper Nile system at that time, connecting to Lake Baringo at the southern end and the White Nile in the north, and that volcanic land adjustments severed the connection. Such a hypothesis explains the Nile species in the lake, such as the crocodiles and the Nile Perch. Lake Turkana (Rudolf) is the most northerly and by far the largest of the Rift Valley lakes. In the north it extends into Ethiopia (Abyssinia) and is 298 Kilometers long, varying in width from 25 to 60 Kilometers. Its maximum depth is about 74 meters. It lies at an altitude of only 382 meters and the surrounding country is semi-desert, but in spite of unfavourable conditions for exploration and its remoteness, the lake itself and the geology of the area around it have been studied by quite a number of scientists. The present basin was formed in Pliocene times, while during the Lower Pleistocene the basin was probably deepened as a result of earth movements. A raised beach at 153 meters was left at this time when the waters of the lake linked up with the White Nile, via the Sobat river. This is known by Dr. Worthington's discovery that Lake Turkana at the present day contains a Nilotic fauna, including the huge Nile perch. Lower Pleistocene lake beds at Omo (just over the Ethiopia -Abyssinian border) and at Gaza (to the east of the lake, in Kenya) yielded a variety of fossil fauna, which has been described by Professor Arambourg. During the Middle Pleistocene faulting took place, while the lake extended to the Lodwar Hills, which now lie more than 65 Kilometers from its western shores, and left raised beaches at 101 meters and 92 meters above present lake level. 68 meters and 28 meters raised beaches bear witness to the height of the lake in Upper Pleistocene times, since when Lake Turkana has been retreating and its alkalinity' increasing. "Along the low-lying western shore of the lake the prevalent S.E. winds have built up a series of sand-pits. . . . During recent years . . . the shore line seems to have changed considerably by the growth of these sand-spits, and probably also by a slight lowering in the general water

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level." There has been renewed volcanic activity near the lake in recent years: the Teleki and Andrew volcanoes near its southern shores have both erupted within living memory. The lake contains three Islands, all of volcanic origin. Central Island has three crater lakes, near which active fumaroles are to be seen. Dr. Worthington comments on the tameness of the crocodiles on Central Island presumably they had never seen man before the Cambridge Expedition to the lake in 1930-31. The most important river flowing into the lake is the Omo, which enters it in Ethiopia (Abyssinian) territory. The other rivers, such as the Turkwel, flow only intermittently through the desert regions bordering Lake Turkana and for most of the year are underground.

Lake Turkana, taken by Adam P G in 2004

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