Coastal Dunes

Coastal Sand Dunes

• https://www.youtube.com/watch?v=t5Q5FFWRxCE (Embed)
• Caption: https://youtu.be/t5Q5FFWRxCE

Formation

• For a sand
• dune to form there
• must be a reliable
• supply of sand, a
• means of transporting it (wind), and somewhere
• for it to be deposited more quickly than it is eroded.
• •The dry grains of
• sand can then be transported by the wind through a process of saltation. If the wind
• blows towards the land, sand will be transported up the beach and beyond the
• high tide mark. When the dry
• particles of sand reach the top of the beach they might be trapped by driftwood
• and rocks.
• If the sands
• is not eroded again, plants might start growing on it increasing the size and
• hence trapping more sand.

Conditions of formation

• Strong onshore
• winds
• Large
• expanses/area of dry sand ( spits, cuspate forelands, bays)
• Reliable
• supply of sand
• Large tidal
• range
• Vegetation to
• act as obstacles to limit/trap sand movement and deposition can occur –
• vegetation cause wind velocity to drop.

Sand Dune Characteristics

• 
• Caption: http://www.s-cool.co.uk/a-level/geography/coastal-processes/revise-it/coastal-deposition

Characteristics of a sand dune

• Embryo – this is the
• first part of the dune to develop and are formed in sheltered areas. Once the
• pioneer plant species such as Lyme grass, sand couch grass and sea rocket
• stabilise, the sand is trapped and accumulated over time - the dune grows.
• Conditions in this dune are dry thus plants adapt by growing long roots and/or
• thorny leaves to reduce evapotranspiration. The early colonising plants will
• eventually die off and decompose. They
• add nutrients to the soil which makes the dunes more hospitable for new and
• larger plants to grow therefore giving them the capability trap more sand –
• larger dunes develop.
• Vegetation
• makes the dunes stable.

Slide 6

• Fore dune – They tend to
• be very yellow as they have limited vegetation so no real humus layers develop.
• Marram grass is the main coloniser and stabiliser.
• Yellow dune – The colour
• darkens as organic material add nutrients and humus to the soil. Sea couch and marram grass stabilise the
• dune.
• Grey dunes – Developing
• humus layers changes the colour of the dune form yellow to grey. Water retention is also increased
• (soil becomes damper and richer) due to more humus therefore more species of plants
• thrive e.g. Creeping willow, red fescue and dewberry. In time, the dune stops growing because the
• sheltered means that there is a lack of wind to blow the sand.

Slide 7

• Mature dunes –
• The dunes can
• sustain more plants such as thistle, evening primrose, bracken, bramble and
• heather because the humus layers grow more. Less than 10% of sand is exposed on
• these dunes.
• Dune slacks - are low lying
• depressions between the dunes. Plants in
• the dune slacks include wild strawberries, buttercup and violets with some flag iris and willow in the
• slacks at the rear of the main dune system. In the slacks, vegetation covers almost
• everything.

Slide 8

• It
• is key to remember that during the development of mature dunes, the embryo
• dunes are continually being formed at the base of the dune system consequently,
• the dune system is advancing seaward.