Sand dunes are ridges or hills of wind-blown sand. They are found at the top of a beach, often extending just inland. Very specialised plants and animals live in coastal dunes, making them a very unique habitat. They are also highly valued for our health and wellbeing, for recreation, and for farming.
The 3Ss: understanding sand dune science
Sand dune are very complex systems where nature and humans interact. To simplify everything, we can focus on three components that are absolutely vital to healthy coastal sand dunes: Sand, Species and Space.
SAND
- Formation of sand dunes
The sand for dunes in Ireland comes from sand made by glaciers that once covered the entire country. Erosion of soft glacial cliffs, the seabed, beaches and dunes releases that sand into the sea. The energy to do this comes from large waves during storms.
After these erosive storm, smaller waves and sea currents bring the sand up onto the beach. Building up the width of the upper beach. - At low tide the beach dries out, and wind blows the sand up the beach.
At the top of the beach, the wind is slowed by obstacles such as seaweed, driftwood and plants. It can no longer carry the sand, and deposits it around these objects building small mounds that we call sand dunes. The small mounds grow as more sand particles are trapped. Plants like Sand Couch or Sea Rocket colonise the mounds, and their roots help to bind the sand together and stabilise the dunes.
Types of sand dunes
Embryo Dunes: Small hummocks of sand that build up on the upper beach. They can be washed away by high tides or storms releasing sand back to the beach, but will form again each year.
Image of Embryo Dune, Roundstone
Foredunes: behind the embryo dune, the foredune often stands a few metres taller, with marram grass stabilising it. These are the most seaward of the main dune field.
Image of Foredune
The stability of foredunes depends on:
- Sand supply and the rate of windblown sand deposit and erosion
- Degree of vegetation cover to help stabilise the foredune
- Frequency and magnitude of storms
Backdunes: These are mature dunes and are furthest away from the beach. As plants die off each winter, nutrient and humus are added to the sand. This developing soil can support more diverse plants, and biodiversity increases, especially around low wetter areas called dune slacks.
Foredune and Embryo Dunes, Donegal
