How does wind shape yardang ridges?
Yardangs are elongated ridges and grooves carved by wind erosion into weak rock or loose sediment, generally aligned with prevailing wind. Their dimensions vary with local material.
Selective erosion
Sand-laden wind abrades the surface, while removal of loose grains deepens grooves. More resistant portions can remain as ridges. Persistent wind direction influences alignment, while fractures and bedding also guide the shape. A yardang should not be confused with a dune deposited by wind.
Identifying them in the field
Parallel ridges provide clues to past winds, but one feature cannot establish a fixed exact direction. Rock resistance and later erosion also affect the pattern. Similar lines on satellite images might result from streams or human activity. Material, erosion marks and landscape context need checking on the ground.