Each column of the pile keeps its own height. A falling grain lands on the column nearest its x-position and adds a small amount of height there. Once a column is taller than its neighbor by more than tan(θ)·Δx — where θ is the material's angle of repose — the excess slides across in an avalanche step, exactly the rule behind cellular-automaton sandpile models.
Fine, dry and damp sand have different real angles of repose (≈30°, 34° and 43°): damp grains stick together from surface tension, so they hold a steeper, taller pile before sliding, while fine dry sand collapses sooner into a shallow cone.
- Drag inside the canvas, or use the position slider, to move the nozzle.
- Turn avalanches off to watch an unrealistic, unboundedly steep pile grow instead.