Dunes and winds interact.

The Namib desert of southern Africa is home to some of the most stunning dunes on Earth. They are primarily linear dunes, which form parallel to the winds that form them. On the left side of the image, the dunes are aligned north-to-south along the direction of the southerly winds that blow through this area. Toward the center of the image, however, the dunes are deflected by strong seasonal winds blowing from the east. On the far right, the dunes break from a linear pattern to one with rectangular criss-crossings. This is a mixture of old and new dunes, evidence that the dominant direction of the wind has shifted over time. (Image credit: NASA Earth Observatory)