Lakes of Ounianga, Sahara Desert
The Lakes of Ounianga consist of 18 lakes located in the heart
of the Sahara Desert, in an extremely arid region of northern Chad
where the average yearly rainfall is no more than 2 mm. They depend on
an underground supply of ‘fossil’ water that fell on this area in
ancient times when the Saharan climate was much wetter than it is today.
Approximately 14,800 to 5,500 years ago the area was occupied by a
single large lake, probably tens of kilometers long. As the climate
dried out during the subsequent millennia, the lake shrank, and large,
wind-driven sand dunes invaded the original depression, dividing it into
several smaller basins. The 18 lakes is all that remains today.
The
lakes are situated in a shallow basin below sandstone cliffs and hills,
from where the ancient water flows. The almost-year-round northeast
winds and cloudless skies make for very high evaporation rates. But the
underground bed of water-rich rocks are large enough to keep supplying
the small lakes with water despite the high evaporation rate.
Remarkably, this unique hydrological system is able to sustain the
largest permanent freshwater lakes to be found in such an arid desert
environment anywhere in the world.
A NASA image taken on November 14, 2009, by the crew of the ISS.
The
lakes are divided into two groups, 40km apart. They vary greatly in
chemical composition, some being so salty that they can only support the
most basic forms of life, while others are fresh enough to provide
habitat for aquatic plants, fish and a diversity of other species. The
largest and most biologically important lake (Lake Teli, in the eastern
group known as Ounianga Serir) has a surface area of 4.4km2 and a
maximum depth of 10 m. Its water is fresh, and supports an abundance of
life. The sandy substrate is highly porous, so water flows freely
underground between Lake Teli and 13 other smaller lakes in the eastern
group.
Further west, across the dunes and sandstone ridges that
characterise this part of the Sahara, the second group of four lakes
(known as Ounianga Kebir) is found, dominated by Lake Yoan (3.6 km2 and
27 m deep). This is a hyper saline lake which supports only algae and a
few other micro-organisms. Rocks around its shores are encrusted in
white salt deposits, and a sprawling village of some 9,000 people is
spread amongst the nearby hills and dunes.
The lakes of Ounianga
form as exceptional natural landscape of great beauty with striking
colours and shapes. Because of its remote location, only a trickle of
fearless tourists (about 500 annually) finds its way to this remote
corner of Chad.
