Add grains of sand to a grid. Any cell with ≥ 4 grains topples — distributing one grain to each neighbor. The system self-organizes to a critical state producing fractal avalanche patterns. Click or drag to add grains.
Grains: 0 | Avalanche size: 0 | Total topplings: 0
Per Bak, Chao Tang, and Kurt Wiesenfeld (1987) introduced the sandpile model as the first example of self-organized criticality (SOC): without tuning any parameter, the system evolves to a critical state with power-law avalanche distributions P(s) ~ s^(−τ), τ≈1.2. The resulting fractal patterns have exact 4-fold symmetry — a consequence of the Abelian property: the order of topplings doesn't matter.