Geomorphology: Solitary wave behaviour of sand dunes

Barchan sand dunes are highly mobile, crescent-shaped dunes that occur in areas where sand is sparse and the wind is unidirectional. Here we show mathematically how two such loose-grained dunes are able to pass through one another while still preserving their shape. The crucial parameters for this solitary-wave behaviour, which is consistent with field observations, are the heights of the two colliding dunes.