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The Seashore

Sand Dunes and Shingle Communities

Sand dunes are accumulations of sand stabilised by vegetation

Namibian dunes

The development of a dune begins with weathering of parent rock. Boulders and stones are ground up into sand by destructive erosive waves and water movements. The resulting sand is deposited on a shore by constructive depositing waves.

The tides recedes and being free-draining, the sand deposited on the shore begins to dry out.

If the shore faces into the prevailing wind the sand grains will be blown inland. Single grains take to the air and hop about 6 metres, they land and dislodge a couple more grains of sand which in turn take to the air and do the same. (You only get dunes forming if the wind direction is right). The process of wind blown grains of sand jumping up the beach is called saltation. Quite often you can see a cloud of sand moving along the beach in this way.

The sand grains blow inland until they meet some form of obstruction. This might be a pile of seaweed dumped high up the shore by the sea, a lump of driftwood, a fence, a pool or muddy, sticky ground. Alternatively, sand might settle in the still air behind a small hillock or similar. The sand piles up against the obstruction and we have the fisrt stage in formation of a sand dune sometimes called an EMBRYO or FOREDUNE .

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