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Wind-formed ripples on the sands of the Merzouga Desert at sunset.
These surface patterns result from consistent wind velocity and grain-size sorting, recording ongoing aeolian processes across the Sahara.
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#Merzouga #Sahara #SandRipples #AeolianProcesses #DesertGeomorphology #SedimentDynamics #NaturalPatterns #EarthScience #Morocco

Waves Over Sand Ripples

Look beneath the waves on a beach or in a bay, and you’ll find ripples in the sand. Passing waves shape these sandforms and can even build them to heights that require dredging to keep waterways passable to large ships. To better understand how the sand interacts with the flow, researchers build computer models that couple the flow of the water with the behavior of individual sand grains. One recent study found that sand grains experienced the most shear stress as the flow first accelerates and then again when a vortex forms near the crest of the ripple. (Image credit: D. Hall; research credit: S. DeVoe et al.; via Eos)

#CFD #computationalFluidDynamics #fluidDynamics #geophysics #granularMaterial #oceanWaves #physics #sandRipples #science #sedimentTransport #sedimentation

Aerial view of sand ripples beneath the water at a beach.

What Makes a Dune?

Wind and water can form sandy ripples in a matter of minutes. Most will be erased, but some can grow to meter-scale and beyond. What distinguishes these two fates? Researchers used a laser scanner to measure early dune growth in the Namib Desert to see. They found that the underlying surface played a big role in whether sand gathered or disappeared from a given spot. Surfaces like gravel, rock, or moistened sand were better for starting a dune than loose sand was. Each of these surface types affected how much sand the wind could carry off, as well as whether grains bounced or stuck where they landed. Every trapped sand grain made the surface a little rougher, increasing the chances of trapping the next sand grain. Over time, the gathering sand forms a bump that affects the wind flow nearby, further shaping the proto-dune. As long as the wind isn’t strong enough to scour the surface clean, it will keep gathering sand as the process continues. (Image credit: M. Gheidarlou; research credit: C. Rambert et al.; via Eos)

#aeolianProcesses #fluidDynamics #geophysics #physics #planetaryScience #sand #sandDunes #sandRipples #science