In the arid Sahara Desert, agricultural development typically occurs in isolated patches. Such development occurs where deep underground water sources have been tapped and/or where sufficient runoff from nearby mountains sporadically supplies water to wadis (ephemeral rivers). In this north-oriented photograph, the latter phenomenon seems to provide life-giving water to the two areas seen on either side of the black massif (or mountain) crossing through the center of this scene. Specifically, two tightly clustered patterns of agriculture, each consisting of a series of dark circles, are located at the base of the massif, one to the north and the other to the south. Each of the black circles is an active agricultural plot approximately 0.8 kilometers in diameter that is being fed by a center-pivot irrigation system.
Massifs like the one in this scene occur throughout the Sahara Desert, where they tend to separate extensive sand seas. The edges of the yellow and orange Ubari and Marzuq sand seas can be seen abutting the dark massif in the north and south respectively. The settlement in the upper right portion of the scene (gray and white, with dark fields) is the Ubari Oasis. This oasis developed along one of the early north-south land routes through the Sahara Desert.
February–March 1990, image STS-36-151-16.