The Great Eastern Rift Valley, a major fissure in the Earth’s crust, extends from the Middle East to Mozambique in east Africa. Lake Natron, one of a series of East Africa Rift Valley lakes resulting from the rifting process, formed as a large block of the lithosphere dropped to create a graben, a trench-like depression. The lake has an exceptionally high concentration of salts and is known as a soda (sodium carbonate) lake. Natron, with its pink color that results from the billions of iron oxide bacteria that inhabit it, is home to enormous flocks of flamingos that congregate to eat the microscopic bacteria that are produced in the alkaline water. Because the shallow lake sits in an isolated drainage basin, the water level and the concentration of soda fluctuate greatly. Visible in the photograph are a small volcano at the north end of the lake and a much larger volcano at the southeast end of the lake. The north-south trending features on either side of the lake are fault scarps that result from the east-west stretching of east Africa.