1. Sand Transport: Wind exerts a force on sand grains lying on the desert surface. When the wind velocity exceeds a certain threshold (typically around 12-15 kilometers per hour), it starts to lift and transport these sand grains. This process is called saltation.
2. Grain Movement: As the wind carries the sand grains, they move in a bouncing or hopping motion close to the ground. This movement allows sand grains to travel short distances (a few centimeters to several decimeters) before falling back to the surface.
3. Collision and Deposition: When the wind-blown sand grains land, they collide with other stationary grains on the ground. This collision dislodges some of these stationary grains, causing them to move and join the saltation process. The continued impact and deposition of these grains, over time, create small mounds of sand.
4. Ripples Formation: As more and more sand grains accumulate on these small mounds, they gradually evolve into larger, regular, and wave-like features known as sand ripples. These ripples usually have a gentle slope on the windward side (facing the wind direction) and a steeper slope on the leeward side (away from the wind direction).
5. Ripple Migration: The wind continues to transport sand grains over the ripples. As the windward slope receives more sand, it gradually grows and advances, while the leeward slope erodes and retreats. This process leads to the migration of the entire sand ripple in the direction of the prevailing wind.
6. Ripple Spacing: The spacing between sand ripples depends on several factors, including sand grain size, wind velocity, and sand supply. Coarser sand grains generally form larger ripples, while finer sand produces smaller ripples. Stronger winds create larger ripples, and a limited supply of sand results in wider ripple spacing.
7. Ripple Patterns: Sand ripples can occur in various patterns, such as straight, sinuous, or branched ripples. The pattern formation is influenced by the interaction of wind flow with the topography and the availability of sand.
Sand ripples are not permanent features and can change shape, size, and location over time as wind conditions and sand availability fluctuate in the desert environment.
