Man enjoying the peaceful sunset at flic en flac. The texture on the sand was formed at low tide by waves movement.
Underwater, whether in rivers or in the sea, sand often forms ripples, like tiny dunes. These ripples, also called ripple-marks, form under certain current conditions and are always perpendicular to the direction of water movement. These ripples are formed according to the same principle as terrestrial dunes: at a certain speed of movement, the fluid covering the sand (air for dunes, water for ripple-marks) carries the grains of sand away and deposits them further, according to their weight. If the movement of the water is due to the swell, the shape of the ripples is symmetrical. We then speak of oscillation ripples. On the other hand, if the movement is caused by a current, the ripples are asymmetrical. The side exposed to the current has a gentle slope, while the side under the current has a steeper slope, as in the case of dunes. These are called current ripples.
Sometimes, under very specific conditions, these marks can become fossilized. The study of the shape of these legacies of the past makes it possible to reconstitute the direction and strength of the currents and swell of environments that have disappeared and to deduce the characteristics of the ecosystems of the time.