Sandpiles have received considerable interest because of their intrinsic scientific interest both from the fundamental and applied points of view, and also because they are simple examples of complex systems whose behavior has been used in an attempt to explain a variety of physical, chemical, biological and social phenomena"

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A 'normal' conical sand pile tends to feature the well known 'avalanche' mechanism (see : Self-Organized Criticalityplugin-autotooltip__plain plugin-autotooltip_bigSelf-Organized Criticality

The term Self-Organized Criticality (SOC) was introduced in a 1987 paper for Physical Review Letters. The groundbreaking research by Per Bak, Chao Tang and Kurt Wiesenfeld (now known as 'BTW') described how complex systems can feature 'critical' points in their development which can lead to sudden, dramatic changes (phase transitions).)

Conventional understanding of sandpile formation is that as grains of sand are poured onto a horizontal surface, a conical pile develops which grows intermittently through avalanches that 'adjust' the angle of repose of the pile about some critical value, or, at least, keep it between two critical values.

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In 1995 however, a newly observed type of sand pile growth was recorded at the University of Havana in Cuba. Involving the so-called 'Sandpile formation by revolving rivers' phenomenon - which has now been replicated and observed in multiple experiments worldwide.

How the revolving 'rivers' emerge, and why they rotate around the pile, is still unknown.

For technical details see :'Sandpile formation by revolving rivers' arXiv: Condensed Matter / 0206493

Note: A video of the phenomenon can be viewed here

Also see : Sand dune formationplugin-autotooltip__plain plugin-autotooltip_bigSand dune formation

"Large swaths of Earth’s surface are covered in loose sediment. The grains that make up this sediment form fascinating bedforms from meandering riverbeds to wavy dunes, whose shapes are constantly changing as water or air currents move the grains.