Migrating sand dunes can encounter obstacles both natural and manmade as they move. Dunes — both above ground and under water — have been known to bury roads, pipelines, and even buildings. A recent experimental study looks at which obstacles a dune will cross and which will trap it in place. Their set-up consists of a narrow channel built in a ring, essentially a racetrack for dunes. Flow is driven by a series of paddles that rotate opposite the tank’s rotation.
The team studied obstacles of different shapes and sizes relative to their dunes, and they found that dunes were generally able to cross obstacles that were smaller than the dune. Obstacles larger than the dune would trap it in place, and, for obstacles close to the same size as the dune, round obstacles were easier to cross whereas sharp-angled ones tended to trap the dune.
The idealized nature of their experiment means that their results aren’t immediately applicable to the complex dunes of the outside world, but the study will be an important touchstone for those predicting dune behavior through numerical simulation. Studies like those require experimental cases to validate their baseline simulations. (Image credit: top – J. Bezanger, figure – K. Bacik et al.; research credit: K. Bacik et al.; via APS Physics)