Merzouga, Morocco The cause of the illusion is the texture and size of the grains of sand. Sand in the Sahara is not only extremely fine but also very small. The Sahara Desert is the world's largest subtropical hot desert and third largest overall (behind the Antarctic and Artic). The desert spans across 11 African countries. Known for its gale force winds that create monstrous sandstorms, the Sahara's dunes are often outrageously high (sometimes at 500 meters).