Swashline

An early evening dog walk along the coast.  As I gazed down into this perfectly crescent-shaped little bay I noticed  foam forming in regular patterns like the scalloped edge of a lace collar as the tide rolled rhythmically in and out. . I wondered how this happens since I know the foreshore here to be smooth and without undulations.

As usual I turned to Prof. Google when I got home and discovered that these shapes are known as beach cusps and have been the subject of scientific debate for a century.  The explanation is a bit technical - something to do with the deposition of sediment - and once formed they are self-sustaining.

You can read about them here and here if you are so inclined.