dîne

Düne is a natural mound or hill of sand formed by wind action. Dünen develop wherever there is a suitable supply of loose sand and sustained wind, commonly along coastlines, river valleys, or desert margins. On coasts, dunes protect inland areas from wave action and storm surges and are a typical feature of the North Sea and Baltic Sea littoral in Germany and other parts of Northern Europe.

Formation and structure: Sand grains are transported by wind by saltation and bounce; when the supply is interrupted by vegetation or moisture, deposition occurs and a dune builds up. The windward slope is gently inclined; the leeward face or slip face is steep. Dune activity changes with wind direction and sand supply; some dunes move over time, others stabilize.

Types: Dünen vary in shape: barchan dunes form crescent shapes with a horn downwind; transverse dunes run perpendicular to prevailing wind; parabolic dunes have vegetation arms; longitudinal dunes run parallel to prevailing winds; star dunes form in multi-directional wind regimes.

Ecology and protection: Dünen host specialized plants such as beach grasses and pioneer species; their roots stabilize sand, while the habitat supports invertebrates and birds. In coastal areas, dunes act as natural barriers and are protected by fences and vegetation management; human activity, storms, and sea-level rise threaten them, prompting restoration and protective zoning.

See also: dune, aeolian processes, coastal management.