Lakes of Ounianga are a series of 18 interconnected lakes in the Sahara Desert, in North-Eastern Chad, occupying a basin in the mountains of West Tibesti and Ennedi East. It constitutes an exceptional natural landscape of great beauty with striking colours and shapes. The saline, hyper saline and freshwater lakes are supplied by groundwater and are found in two groups 40km apart. Ounianga Kebir (The Great Ounianga) comprises 4 lakes, the largest being Yoan. Its highly saline waters only sustain algae and some microorganisms. The second group, Ounianga Serir (The Little Ounianga), comprises 14 lakes separated by sand dunes. With their high quality freshwater, some of these lakes are home to aquatic fauna, particularly fish. At 436 ha, Lake Téli has the largest surface area but is less than 10m deep.
These lakes form a hydrological system that is unique in Earth’s deserts. Ordinarily when water is exposed in highly arid environments it becomes saline due to a high rate of evaporation. In this case, unique physical factors combine to keep all of the lakes, except the central Lake Téli, fresh. First, water accumulated in an underground aquifer is supplied to the lakes. Second, wind blown sand separates the basin into 10 lakes with Lake Téli occupying a lower position. Third, thick mats of reeds cover the surface of the fresh water lakes, where they slow evaporation, but are absent from the saline waters of Lake Téli. As a result, greater evaporation keeps its water level low. This allows water from the adjacent lakes to flow through the permeable dune barriers into Lake Téli keeping their waters fresh.
About the stamp
The stamp depicts Lilian Thuram, a retired professional football defender and the most capped player in the history of the France national team.
Lakes of Ounianga - Wikipedia
Lakes of Ounianga - UNESCO official website
Sent from N'Djamena (Chad), on 27.01.2015
Photo: S. Kropelin