dune geomorphology

dune succession

dune glossary

Dunes

Dunes form along a coast when deposition by wind on the upper beach develops low mounds and ridges that stand above the limit of wave action. Pioneer species colonise and bind these embryo dunes and allow the retention of some moisture. Marram then gains a foothold and its shelter leads to the trapping of more sand and the eventual emergence of fully-developed dunes.

In a typical dune system the active fore-dunes are succeeded inland by the first dune ridge. Older ridges become lower and flatter as fresh sand supplies are usually trapped in the younger dunes and sand is removed from the older dunes to fill the valleys between dune ridges. Older dune systems originally give way inland to links, where a heavily-grazed turf is developed on stabilised sand sheets. In Scotland, these links form the base for many a golf course.

In the slacks between the dunes the water table rises close to the surface. The lowest slacks are inundated at spring tides and trash lines mark the tidal limit. These areas support a diverse flora of calcium-loving plants. Eventual decay leaves behind peat and soil layers with root horizons.

Dunes have a long history of erosion in rising seas. The recycling of sand may allow the development of new dune systems at adjacent sites or the migration inland of the entire dune sequence. Where dune faces have been eroded, the complexity of dune history is laid bare, with buried organic layers marking periods of stability, vegetation cover and soil formation and cross-bedded sands representing periods of dune migration.