Dunes

Dunes are mounds or ridges of loose, wind-blown sand that form in areas where sand supply is high and the surface is stabilized long enough for deposition to occur. They occur in deserts, along coastlines, in river valleys, and in some inland regions. Dune fields vary in size from a few meters to tens of kilometers and can migrate over time as winds move sand from one place to another.

A dune’s basic structure includes a windward slope, a crest, and a lee or slip face where sand avalanches down at the angle of repose. Dunes grow as sand accumulates on the windward side and can advance or shift position when wind patterns persist. The angle of repose for dry sand is typically around 30 to 34 degrees.

Common dune types include barchans, crescent-shaped dunes with horns pointing downwind that form under unidirectional winds and limited sand supply; transverse dunes, which form as broad ridges perpendicular to the wind where sand is plentiful; longitudinal dunes, which run parallel to the prevailing wind; star dunes, with multiple arms created by multidirectional winds; and parabolic dunes, which are crescent-shaped and often stabilized by vegetation.

Distribution and ecology: Dunes host specialized plants and animals adapted to shifting sands and arid conditions and can play a protective role by trapping sediments and stabilizing coastlines. Human activity, such as development, tourism, and grazing, can threaten dune integrity, underscoring the need for careful management.

Movement and management: Dunes migrate with prevailing winds, influenced by wind strength, sand supply, moisture, and vegetation. Management approaches range from stabilization through vegetation planting and sand fencing to preserving mobility in areas where dune dynamics support ecological or geomorphological goals.