This image of the southern half of Lake Natron shows the characteristic colors of lakes where very high evaporation occurs. As water evaporates during the dry season, salinity levels increase to the point that salt-loving organisms begin to thrive. Salt-loving organisms include some cyanobacteria, tiny bacteria that grow in water and make their own food with photosynthesis as plants do. The red pigment in the cyanobacteria produce the deep reds of the open water of the lake, and orange colors of the shallow parts of the lake. In the inset, numerous, near-white salt-crust “rafts” pepper the shallowest parts of the lake. Bright white clouds are also visible just right of center and on the top margin. The lake is quite shallow, less than three meters deep, and varies in width depending on its water level. In this image, the lake is about ten kilometers wide. Tan lines run north-south, parallel to the eastern lake shore on the right side of the image. Called fault scarps, these lines are the steep, step-like slopes created when the land was pushed up during earthquakes along faults in the Great Rift Valley system of East Africa. Also part of the rift system is Gelai Volcano, the slopes of which appear in the lower right corner.
The four main environments typical of salt (alkali) lakes in East Africa are illustrated well in the image. The delta of one of two dominant streams that flow into the lake (top left) shows where fresh water enters the basin. Open water, salt flats with salt crusts, and mud flats succeed each other in a west-to-east progression towards the shallow side of the lake. Vast numbers of the pink Lesser Flamingo (2.5 million by one calculation) rely on Lake Natron as their only breeding ground in the Rift Valley. The flamingoes feed on the nutrient-rich cyanobacteria. As salinity increases, so do the number of cyanobacteria, and the lake can support more nests. Threats to the salinity balance from increased fresh water influxes will come from projected logging in Natron watersheds and a planned hydroelectric power plant. Although development plans include construction of a dike at the north end of the lake to contain the fresh water, the threat of dilution to this breeding ground may still be serious. The government of Tanzania recognized both the threat and the uniqueness of the habitat in 2001, when it placed Lake Natron on the list of Wetlands of International Importance as part of the Ramsar Convention, an intergovernmental treaty meant to protect wetlands.
Images of Lake Natron from four other dates can be seen on the Earth Observatory and associated links. The area and shape of the open water and salt-raft zones depend on lake levels, controlled mainly by local rainfall and evaporation. Patterns of these sub-environments therefore appear different across the span of a few years.
Astronaut photograph ISS012-E-20456 was acquired March 15, 2006, with a Kodak 760C digital camera using a 400 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.
If Lake Natron, in Africa’s Great Rift Valley, had a color theme, it would be pink. The alkali salt crust on the surface of the lake is often colored red or pink by the salt-loving microorganisms that live there. Also, the lake is the only breeding area for the 2.5 million Lesser Flamingoes that live in the valley. These flamingoes flock along saline lakes in the region, where they feed on Spirulina, a blue-green algae with red pigments. This mosaic of photographs of the southern portion of Lake Natron shows the largest open lagoon area, and island mud flat, and a large area of pink salt crust. The colors show the actual colors viewed by the astronauts. Each time the lake is photographed, there are differences in the pattern of its salt crust, and the red colors of the blue-green algae and bacteria on the surface of the crust.