Watch a barchan sand dune sculpt itself from a random heap into its familiar crescent profile, then slowly walk across the desert as wind erodes its gentle windward slope and deposits sand on its steep lee face. Adjust wind speed, wind direction, and vegetation cover to see how each factor changes the dune's shape and migration rate.
Aeolian (wind-driven) sand transport: saltation erosion on the windward slope, downwind deposition, and slope relaxation at the angle of repose (~34°) that carves the dune's characteristic steep slip face.
Raise wind speed to speed up migration, flip wind direction to see the dune reverse course, and increase vegetation cover to anchor the dune and slow it down.
Barchan dunes are the fastest-moving dune type on Earth — and have even been observed on Mars, where thin air still manages to sculpt the same crescent shapes.
This simulation recreates aeolian (wind-driven) sand transport across a barchan dune, rendered as a cross-sectional heightfield of roughly 200 columns spanning about 100 metres of desert. Each simulation step, wind erodes sand from the gentle windward slope in proportion to wind speed squared and local steepness — a simplified stand-in for the way shear stress drives saltating grains into hopping motion. That sand is carried a short hop downwind and deposited on the lee side, building up the dune's steep slip face.
Whenever a slope exceeds the sand's natural angle of repose of about 34 degrees, an avalanche pass slides grains downhill until the slope relaxes back to that limit, which is exactly why real dune slip faces are so consistently steep. Left alone, an initially random mound of sand self-organises into the familiar asymmetric crescent profile and then slowly crawls downwind as erosion and deposition repeat, cycle after cycle. Vegetation cover pins sand in place and can dramatically slow or halt this migration, which is why re-vegetation is a real-world strategy for stabilising encroaching dune fields near roads, farmland and villages.
What does this simulation show?
It models how wind erodes sand from the gentle windward face of a dune, carries it downwind in short hops, and deposits it on the steep lee face, gradually reshaping a random sand pile into a classic barchan dune profile that migrates across the desert.
Why does the dune have a steep side and a gentle side?
The gentle windward slope is where wind constantly erodes and pushes sand forward. The steep lee face, called the slip face, forms because sand piling up there quickly exceeds the angle of repose and avalanches downhill, settling at a stable angle of roughly 34 degrees.
How fast do real sand dunes migrate?
It varies widely with wind strength, sand supply and dune size. Small, sand-starved barchan dunes can migrate tens of metres per year, while large dunes with more sand mass typically move much more slowly, sometimes only a few metres annually.
Wind speed controls how much sand is eroded and how far each hop carries it downwind, directly setting the migration rate. Wind direction flips which slope faces the wind, reversing the direction of migration. Vegetation cover seeds plants that resist local erosion, anchoring sand and slowing the dune's movement.
Saltation is the dominant mode of wind-driven sand transport: grains are lifted briefly into the airflow, carried a short distance, and land with enough force to kick up more grains. This bouncing, hopping motion is what the simulation approximates as short downwind "hops" of eroded sand.
Plant roots and stems physically trap sand grains and disrupt the near-surface wind flow that would otherwise pick them up, sharply reducing erosion. Where vegetation cover is high enough, dunes can become fully stabilised and stop migrating altogether, which is why coastal and desert land managers plant vegetation to control dune movement.
It captures the core real physics — wind-speed-dependent erosion, downwind saltation transport, and slope relaxation at the angle of repose — using a simplified cellular heightfield model rather than a full fluid-dynamics simulation. The qualitative behaviour, including barchan self-organisation and vegetation anchoring, matches real dune science.