The wind blows ripples into sand dunes in the Lake Mungo lunette. Millions of sand grains being blown up the windward surface of a dune form a series of ridges and troughs called wind ripples. The bouncing sand grains tend to land on the windward side of each ripple creading a low ridge. The spacing of the ridges and troughs is related to the average distance grains jump and is determined by by the wind velocity and grain size. The dunes stretch in a continuous arc for approximately 40km. NSW, Australia.