Jewel of the Kalahari Desert

This short focal-length astronaut photograph shows the entire Okavango “delta,” a swampland known in southern Africa as the “Jewel of the Kalahari Desert.” This enormous, pristine wetland almost miraculously appears in a desert where surface water is typically non-existent. The water comes from the Okavango River, which rises in the high-rainfall zone of southern Angola, hundreds of kilometers to the northwest.

The dark-green forested floodplain is about 10 kilmeters (6 miles) wide where it enters the view (image left). The Okavango then enters a rift basin, which allows the river to spread out and form the wetland. The width of the rift determines the dimensions of the delta—150 kilometers (90 miles) from the apex to the downstream margin (image right). The apex fault is difficult to discern, but two fault lines define the downstream margin; the faults appear as linear stream channels and vegetation patterns oriented at right angles to the southeast-trending channels at image center.

The channels carry sediment from the Okavango River that is deposited within the rift basin. Over time, a fan-shaped morphology of deposits has developed, leading to characterization of the wetland as the Okavango “delta.”

The greens of denser savanna vegetation in the north give way to browns of the open “thornscrub” savanna to the south, matching the precipitation patterns of higher rainfall in the north and less rainfall in central Botswana. More subtle distinctions also appear: the arms of the delta include tall, permanent riverine forest and seasonal forest (dark green), with grasses and other savanna vegetation (light green) on floodplains.

Linear dunes, built up by constant winds from the east during drier climates, appear as straight lines at image left. The dunes are 10 meters high, and their sands hold enough moisture for some trees to grow on them. Counter-intuitively, the low “streets” between the dunes are treeless because they are dominated by dense, dry white soils known as calcretes.