There are but a handful of places where the Rift Valley evokes its geographically violent origins with graphic immiediacy. Ethiopia’s Danakil Desert is one such spot; the volconic Virunga Range in the Albertine Rift is another. And so, too, is the most northern landmark in the Tanzania Rift Valley, the low-lying Lake Nitron, a shallow silver of exceptionally alkaline water that extends southwards from the Kenyan border near Mount Shompole from 58 km. The Natron skyline is dominated by the the textbook volcanic silhouette of Ol Doinyo Lengai, which rises more than 2 km above the surrounding Rift Valley floor to the an altitude of 2,960 m, its harsh black contours softened by an icing of white ash that glistens brightly below the sun, as if phenomenon whose caustic waters are enclosed by a crust of sodden grey volcanic ash and desiccated salt, punctuated by isolated patches of steamy, reed-lined swamp where the hot springs that sustain the lake bubble to the surface. Thought to be about 1.5 million years old, Natron is a product of the same tectonic activity that formed the Ngorongoro Highlands and Mount Gelai, the latter being a 2,941-metre-high extict volcano that rises from the eastern lakeshore. Nowhere more than 50 cm deep, it has changed shape significantly since that time, largely as a result of volcanic activity associated with the creation of Ol Doinyo Lengai to its immediate south. It lies at an altitude of 600 mm in an unusually arid stretch of the rift floor, recieving an average of 400 mm of rainfall annually, and it would have probaly dried out centuries ago were it not also fed by the freshwater Ewaso Ng’iro River, which has its catchment in the cenral Kenyan Highlands, and the hot springs that rise below its floor. he alkaline level has also increased drastically over all mellennia, partially because of the high salinity of ash and lava dposites from Lengai, partially because the lake’s only known outlet is evaporation. Today, depending on recent rainfall, the viscous water has an average pH of 9-11, making it mostmas caustic as ammonia when the level is very level, and it can reach a temperature of up to 60°C extreme circustances.

FAUNA

The area around Lake Natron supports a thin population of large mammals typical of the Rift Valley. Zebra anf giraffe are quite common in the vicinity of Engaresero, and other wildlife includes wildebeest, zebra, fringe-eared oryx, Grant's and Thomson’s gazelle, and even the odd lion and cheetah. Natron's hypersalinity makes it incapable of sustaining any but most specialised life forms. The only resident vertebrates are few species of small fish, notably the endemic white-lipped tilapia that congregate near hot-spring inlets where the water temperature is around 36 to 40°C. The microbiology of the lake is dominated by halophytic organisms such as spirulina, a form of blue green algae whose red pigments make the salt-encrusted flats in the centre of the lake look bright red when seen from the air. Lake Natron is also the only known breeding ground for East Africa’s 2.5 million lesser flamingos, which usually congrate there beween August and October, feeding on the abundant algae. The breeding ground’s inhospitality to potential predators makes it an idal flaming nursery, but it also makes it difficult for human visitors to access-situated in the centre of the lake, it was discovered as recently as the 1950s and it can only be seen from the air today. In addition to the flamingo, Nitron attracts up to 100,000 migrant water birds during the European winter.

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