Dune quiz

What's wrong with the sign above? In the recent issue of Geology Today, Tony Waltham of Nottingham Trent University wrote about this roadside sign he had encountered in Oman, warning of dune encroachment. However, there's a slight error - clues in the inset photograph of barchans on the march across vehicle tracks and my own picture from Egypt's Western Desert below.

Comments

[Callan Bentley]

The cartoon barchan is moving in the wrong direction!

[Sandglass]

Absolutely correct! And the grand prize is ..... ah, sorry, forgot to arrange for a prize, but will do so next time. Barchan dunes migrate in the direction that the "horns" are pointing, so on the sign, the dune has already cleared part of the road and is moving off to the left. Tony Waltham speculates that, artistically, the imminent encroachment of a couple of dune tips does not seem adequately threatening; the full force of the rear of the dune seeming to be flying backwards on to the road is much more dramatic - but wrong.