Two tourist lessons in sand dynamics

A few days ago, I described the fractal sand landscapes on the beach of Cap Ferret on the Atlantic coast west of Bordeaux. The swirling sand banks that shape-shift around the cape are but part of the great drama of shifting sand around the Bay of Arcachon and southwards past the great dune of Pyla, the largest in Europe. I left Cap Ferret and navigated around the bay to visit the dune where I found a tourist attraction not much less teeming than that of Mont-Saint-Michel (my previous post). Getting to the dune required passing through endless stalls selling the predictable claptrap and tat, but I did find a good selection of postcards that showed aerial views of the dune and the offshore sandbanks. I bought several, but it was only later, when I laid them out, that I realised how vividly they illustrated the real-time dynamics of this great sand system. Each postcard view was taken at a different time (although, irritatingly, not documented) – and every one is visibly and dramatically different. One is shown at the head of this post, the others below, together with the Google Earth view – a lesson in the futility of nautical charts in the arenas of the great games that sand plays.

I also found, amongst the claptrap, large numbers of “sand picture” souvenirs, plastic rotatable frames within which lurid varicoloured sand is set in an oil of some kind – a sort of arenaceous lava lamp. Turn the frame and the sand drifts down to create a new “landscape.” I bought one of the least lurid and I have to admit that I have enjoyed experimenting with it. As shown below, I have created some vivid cross-bedding reminiscent of my kitchen physics experiments I described back in April. So, search among the tourist tat and you can find lessons in marine sand dynamics and the behaviour of granular materials!