The microbiology of the lake is dominated by salt-loving 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. The only resident vertebrates are a few species of small fish, notably the endemic white-lipped tilapia that congregate near hot-spring inlets where the water temperature is around 36–40☌. Natron’s hyper-salinity makes it incapable of sustaining any but the most specialised life forms. Today, depending on recent rainfall, the viscous water has an average pH of 9–11, making it almost as caustic as ammonia when the level is very low, and it can reach a temperature of up to 60☌ in extreme circumstances. The alkaline level has also increased drastically over the millennia, partially because of the high salinity of ash and lava deposits from Lengai, partially because the lake’s only known outlet is evaporation. Nowhere more than 50cm 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. 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 2,941m-high extinct volcano that rises from the eastern lakeshore. Then there is the lake itself, a thrillingly primordial 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. The Natron skyline is dominated by the textbook volcanic silhouette of Ol Doinyo Lengai, which rises more than 2km above the surrounding Rift Valley floor to an altitude of 2,960m, its harsh black contours softened by an icing of white ash that glistens brightly below the sun, as if in parody of Kilimanjaro’s snows. And so, too, is the most northerly landmark in the Tanzanian Rift Valley, the low-lying Lake Natron, a shallow sliver of exceptionally alkaline water that extends southward from the Kenyan border near Mount Shompole for 58km. Ethiopia’s Danakil Desert is one such spot the volcanic Virunga Range in the Albertine Rift is another. There are but a handful of places where the Rift Valley evokes its geologically violent origins with graphic immediacy.
0 kommentar(er)
