Physicists have unraveled how certain wind-driven sand dunes in Morocco and Peru apparently tunnel through slower dunes.
Barchan dunes are massive, crescent-shaped sand piles that move across wind-swept deserts at speeds up to tens of meters per year. Because smaller dunes outpace bigger dunes and eventually appear in front of them, the small dunes seem to be punching through big ones.
Such behavior has precedents: Solitary waves of light, sound, or water that pass directly through each other are known as solitons (SN: 11/20/99, p.327). Now, a new mathematical model for wind-driven sand, as well as computer simulations of the same, reveal that one Barchan dune can, indeed, act as a soliton and pass through a slower-moving dune.