While wave-formed ripples are traditionally described as symmetrical, asymmetric wave ripples are common in shallow waters along sandy shores. They are produced by bottom oscillations generated by passing breaker waves, which have unequal intensity in opposite directions.

Where do ripples form?

Sometimes tiny ripples form on silty sediment, and larger dunes form where very fast water currents flow over gravel. Ripples and dunes are useful because they are fairly commonly preserved in the sedimentary record. Assymetrical ripples and dunes form when current flows in a single direction, as along a river bottom.

How are symmetric ripples formed?

Symmetric ripples are formed by bidirectional currents: currents that move in one direction and then in the opposite one. Does it ring a bell? Waves! Waves cause ripples to be symmetric because both sides of the ripple become alternatively sites of erosion and deposition while water moves back and forth.