Marine processesCoastal sand dunes

HMMMM SAND DUNES....??

Sand dunes are small ridges or hills of sand found at the top of a beach, above the usual maximum reach of the waves.

Dunes form where constructive waves encourage the accumulation of sand, and where prevailing onshore winds blow this sand inland. There need to be obstacles—for example, vegetation, pebbles and so on—to trap the moving sand grains. As the sand grains get trapped they start to accumulate, starting dune formation.

HOW EXACTLY ARE THEY FORMED?

oAt low tide, deposits of sand in the inter-tidal zone (between the high and low tide marks) may be exposed and start to dry. The dry grains of sand can then be transported by the wind (by saltation). oWhen the dried sand reaches the top of the beach it can be trapped by debris such as driftwood, dead seaweed or rocks and pebblesoIf the sand is not eroded again it may become colonised by small plants, or trap other windblown debris, increasing its size and thus trapping even more sand. oAs the dunes grow in size they are able to catch more of the sand blown across them by the wind. o. Firstly the roots bind the sand together, and secondly the above ground vegetation traps particles of sand as they are blown over the surface.

THEY M

OVE TO

O!

Interestingly, dunes move slowly. This occurs when the wind lifts sand up on the windward side and the sand falls down on the leeward side.

In this picture, the wind is blowing from right to left and sand is therefore carried from the windward side of the sand dune, to the leeward side: Hence, the sand dune would move or migrate over time.

Greatstone, USA

Wooden path over the  sand dunes to the blue sea and fluffy white clouds at Swansea.

Florida Beach, Sand Dunes and Sea Oates

northwestern Florida coast of Gulf of Mexico

Cronulla Dunes, Kurnell Peninsula, New South Wales, Australia.

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PRESENTATION BY DAISY SOWAH,THANK YOU FOR YOUR TIME

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