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By David Adam

Alex Noriega

THE Israeli city of Ashdod has all the features found in a modern metropolis. Shopping malls, theatres, nightclubs, bars, plenty of good schools. But there is something else, too. Every weekend, at least in normal times, its citizens grab their buckets, spades and quad bikes and head for the city’s most unexpected attraction: the biggest urban sandpit in the world.

Ashdod’s Big Dune, up to 35 metres high and with the footprint of a dozen football pitches, dominates the city’s largely undeveloped neighbourhood 14. One of the last remnants of the region’s original coastal landscape, it isn’t just a much-loved urban talking point, but also a dramatic example of a long-standing mystery. As bizarre as it sounds, scientists aren’t sure how it got there – or indeed why any of the world’s sand dunes exist.

On one level the answer to that question is obvious: the wind blows individual sand grains into piles. But exactly how and why dunes form in the way they do still eludes us. Now efforts to get to the bottom of this are taking on a new urgency, and not just because they could solve what Nathalie Vriend at the University of Cambridge explains is a “fundamental physics problem”. As more human developments push into desert terrain and parts of the world grow drier due to climate change, the race is on to better predict the paths of shifting sands.

Karol …