A desert sand dune is a sort of slow-motion wave; formed by the action of wind on sand, dunes grow and shift over time and can engulf roads, farmland and even towns. New techniques aim to stop sand dunes by harnessing the wind that forms them.

Walls or fences to block dunes soon get overwhelmed. Traditional methods of stabilisation include planting vegetation (which can get buried in a moving dune) or spraying with tarry crude oil.

A more sophisticated technique developed by French scientist Jean Meunier uses low plastic fences to channel the movement of sand. Wind-blown sand stays close to the surface, moving in small hops (saltation) or rolling along (reptation). Each saltation sets 10 other sand grains reptating, so even a 2ft fence catches practically everything. A sand dune is in a constant state of erosion and deposition, and the fences can direct growth and increase erosion. Carefully placed low fences cause swirling eddy currents in the wind, breaking up the dune beyond them. Meunier has even shown how a V-shaped fence can "guillotine" a dune in half: it can reduce a 5 metre high dune to a flat sandy plateau in two months, leaving a surface which can be stabilised relatively easily with vegetation.

The United Nations Environment Programme is now sponsoring further research. Dunes may be eventually defeated by a few plastic sheets and a little ingenuity - and the help of the wind.

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