Some 20 million years ago, the earth's crust weakened and tore itself apart creating a jagged rift, thousands of kilometers long, across the African continent. The land on either side erupted creating great volcanic mountains, while the valley floor gradually sank into a low flat plain.

This geologic phenomena, dubbed the Great Rift Valley by the Scottish explorer John Walter Gregory, divides Kenya neatly down the length of the country essentially separating east from west. Today's Rift Valley is characterized by uninhabitable desert and fertile farmland, flat arid plains and steep escarpments.

In some places this natural divide is up to 100 km (60 miles) wide, while it reaches its narrowest point just north of Nairobi at 45 km wide. The valley floor is at its lowest near Lake Turkana where there is virtually no distinction between the Great Rift and the surrounding desert.

As it heads south, however, the valley walls form sheer cliffs rising to 1,900 km (6,232 ft) at Lake Naivasha. After Naivasha, the valley descends again to 580 meters (1,902 feet) at the Tanzanian border. Subterranean movement is common today as the Rift Valley is home to thirty active and semi-active volcanoes and countless hot springs along its length. This string of alkaline lakes and boiling springs northwest of Nairobi includes Lake Baringo, Lake Bogoria, Lake Nakuru, Lake Elementaita, Lake Naivasha, and Lake Magadi in the south.

These lakes are unique because their water is highly concentrated sodium carbonate. This situation is caused by the high alkalinity from the surrounding volcanic rocks coupled with poor drainage outlets due to the steep sides of the valley. The high evaporation of the surface lake water results in sodium carbonate which, in turn, creates an ideal breeding ground for algae. Several species of fish, tilapia in particular, thrive in this environment. As a result, millions of birds flock to these soda lakes to feast on the abundant food supply of algae and fish. Each of the lakes in the Rift Valley string have a slightly different water composition ranging from freshwater to extremely alkaline, highly saline to brackish.