Coastal Dunes

Slide Set by chidat, updated more than 1 year ago
Created by chidat almost 4 years ago


Coastal Land forms: Dunes

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    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.

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    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. 
    Conditions of formation 

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    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.
    Characteristics of a sand dune

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    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.

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    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.

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     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.
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