A dune is an accumulation of sand in the deserts that are generate by the wind so this is why they have this shapes,they are produced by the wind changes or because of the variation of the amount of sand.When the wind has a dominantdirection, the dunes have a C shape; the advance direction of the dunes is the factor that decides the huge. The small one are the one that go faster, the highest dunes are the one that are 4 or 6 meters. This kind of dunes and these movements you can see in Sechura desert (In Peru).

The movements of the dunes can cause big problems like: the invasion of villages, towns, roads, fields... the best way to control this invasions is to plant trees next and over the dune, other possibility is to spray materials like petrol or some used oils. The first village to do this was the town of villa Gesell in Bonaernse and rhe man who did this kind of experiments was Carlos Idaho Gesell in the Uruguay cost, nowdays cover by pinewoods. But in Spain there some examples too, like Barbate´s pinewood.

What would you do is you where in a village near a dune, and you know that in some moment the dune would invade your house?
This question was the principal one when in 19 century in Barbate the villagers has to plant pines covering a dune.