How Coastal Sand Dunes Form Over Time

By Using a Map and Compass on Coastal Paths
Comments 35
31 Jul 2026

How Coastal Sand Dunes Form Over Time

The journey begins with a grain of sand

Every dune system on the British coast starts with dry sand on a wide, flat beach. When the tide retreats and the wind picks up, grains are pushed inland. They bounce and skip in a process called saltation, travelling low to the ground. The best conditions are a strong onshore wind, a generous supply of sand, and a beach wide enough to let the sand dry between tides.

At the top of the beach, the first obstacle — a clump of seaweed, a piece of driftwood, or a tuft of sand couch — slows the wind. Sand piles up around it. That small heap is an embryo dune. It might only be a few centimetres high, but it is the beginning of a ridge that could last for centuries.

From embryo dune to foredune: the first plants

Embryo dunes are fragile. They are flooded by spring tides, scoured by winter storms, and rarely last long. But if they survive a season or two, plants arrive. Sand couch and sea rocket are pioneers, germinating in the bare sand. Their roots and shoots slow the wind further, and the dune grows.

Behind them comes marram grass, the great builder of British dunes. Its long, tough leaves bend with the wind, and its underground rhizomes spread horizontally, sending up new shoots as sand buries them. Marram can cope with being buried by a metre of sand in a year. As it grows, it traps more sand, and the embryo dune becomes a foredune — a continuous ridge facing the sea.

Foredunes are yellow dunes: the sand is still raw, low in nutrients, and full of shell fragments. They can rise by several centimetres a year. A single marram tussock can build a mound a metre high over time.

Yellow dunes, grey dunes and the march inland

As you move inland, the dunes change. The next ridge is older, higher, and more stable. Marram still dominates, but mosses, lichens and small grasses appear. The sand darkens as organic matter accumulates. These are yellow dunes turning grey.

Further back, grey dunes are fixed by a carpet of mosses, lichens, and grasses such as sheep's fescue and sand sedge. The soil is richer, though still limey and free-draining. Wildflowers arrive: pyramidal orchid, bee orchid, common restharrow, and sea holly. The dune surface is no longer bare.

Between the ridges lie dune slacks — damp hollows where the water table reaches the surface. They flood in winter and dry in summer, supporting a completely different community: creeping willow, marsh helleborine, grass of Parnassus, and rare dune gentian. Slacks are often the richest part of a dune system for wildlife.

Reading the landscape: ridges, slacks and blowouts

Each ridge in a dune system marks a former shoreline. On a prograding coast — one where sand is still being added — you can walk from the youngest foredune near the sea to older, inland dunes that may be centuries old. The pattern is a record of slow, shifting growth.

But dunes are not static. Winter storms cut into the seaward edge, creating blowouts — hollows where wind has scoured sand down to the water table. Blowouts can be dramatic, but they are also part of the cycle. Marram and sand couch recolonise them, and new dunes form. On eroding coasts, the whole system may roll inland, with new dunes building behind old ones as the front is lost to the sea.

When you walk, look at the shape of the land. A ridge running parallel to the shore is a dune line. A gap between ridges is likely a slack. A steep, raw face of sand is a blowout or a dune edge. Reading these features turns a simple walk into a lesson in geology and time.

Wildlife to look for on a dune walk

British dunes are havens for specialised wildlife. The mix of bare sand, short turf, tall grass, and damp slacks supports species found nowhere else.

Natterjack toad: rare, mainly in north-west England and Scotland. Breeds in shallow, warm pools in dune slacks. Listen for the male's loud, rasping call on spring evenings.
Sand lizard: found on some dune systems in north-west England and Wales. Needs bare sand for basking and egg-laying.
Skylark: nests in short grass on the dunes. Its song is a cascade from high in the sky.
Ringed plover and little tern: nest on the beach and foredune. Keep your distance between March and July.
Northern dune tiger beetle: a fast, metallic-green predator of bare sand. Look for it on sunny days.
Grayling butterfly: rests with wings closed, showing false eye-spots. Found on dry, flower-rich dunes.

Walking the dunes well: tides, paths and timing

A dune walk is best planned around the tide. Check a local tide table and aim for low water, when the beach is widest and the sand is dry. Onshore winds are what build dunes, but they can also whip sand into your face — a pair of sunglasses and a buff help.

Stay on marked paths where they exist. Dune vegetation is easily trampled, and compacted sand loses its ability to trap more. Ground-nesting birds are vulnerable: a single dog off the lead can flush a sitting ringed plover and leave eggs to chill. Keep dogs under close control, and on a short lead in spring and summer.

Take binoculars and a hand lens. Look for tracks in bare sand: fox, rabbit, and the drag marks of a natterjack toad. In winter, dunes are quieter but still alive with wintering thrushes and owls. Storms may reshape the coast, but the slow work of wind and marram continues. Every walk is a snapshot of a system that is always growing, always shifting.

Dune Ecology

Capturing Wildlife Without Disturbing Dune Habitats

This waymarked route crosses boardwalks, grassland and a quiet beach. Expect seals offshore and skylarks singing above open dunes.

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5 Comments

Robert Sonny says Jul 21, 2024 at 10:00am

I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
Reply
- John Abraham says Jul 21, 2024 at 10:00am
  
  I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
  Reply
  - Robert Sonnysays Jul 21, 2024 at 10:00am
    
    I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
    Reply
Robert Sonny says Jul 21, 2024 at 10:00am

I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
Reply

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