These are crescent-shaped sand dunes. The sand is slightly dark, compared with the soil surrounding the dunes. These dunes are highly magnetized volcanic ash, which explains why the particles tend to fall back on the dunes instead of being blown away by the wind.
When strong winds blow, these sand dunes, also known as barchan, begin to move. Slowly but surely, they travel through the desert, at an average of 55 feet (17 meters) a year. It’s estimated that these shifting sand dunes have been wandering the savannah for 3 million years.