Uphill solitary waves in granular flows
  We have experimentally observed a new phenomenon in the surface flow of a granular material. A heap is constructed by injecting sand between two vertical glass plates separated by a distance much larger than the average grain size, with an open boundary. As the heap reaches the open boundary, "soliton-like" fluctuations appear on the flowing layer, and move "up the hill" (i.e., against the direction of the flow). We explain the phenomenon in the context of stop-and-go traffic models, and show that soliton-like behavior is allowed within a Saint-Venant description for the granular flow. 
E. Martinez, C. Perez-Penichet, O. Sotolongo-Costa, O. Ramos, K. J.   Maloy, S. Douady and E. Altshuler