Lost in a nondescript part of the savannah, near the Olduvai Gorge on the road to the Serengeti, are two crescent-shaped sand dunes. The sand is remarkably dark, especially in comparison with the soil surrounding the dunes. This is because it is highly magnetized volcanic ash, which explains why the particles tend to falls back on the dunes instead of being blown away by the wind.

In fact, it is possible to throw a handful of sand in the air and see how it clamps together and re-joins the dunes. However, when strong winds blow, these sand dunes, also known as barkan, 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.

Although this phenomenon is rare, it is not completely unique, and its origins have been ascertained. If volcanic ash is rich in iron, it can become magnetized, and when it is blown by the winds, it may start collecting around a rock. Given a sufficient amount of time, this little mound can become a dune.

The local Maasai people believe the shifting sand dunes have come from the nearby sacred mountain Ol Doinyo Lengai, loosely translated as the Mountain of God (where God resides). As a consequence, these dunes are also considered sacred by the Maasai, who convene by the dunes in cases of prolonged draught. On these occasions, a goat is sacrificed to the gods so that rain may come soon. Understandably, climbing the sand dunes is inappropriate.