Drop grains one at a time. When a cell reaches threshold 4, it topples — distributing 1 grain to each neighbor. The group structure of recurrent states is abelian: toppling order doesn't matter.
Grains dropped: 0
Total topplings: 0
Last avalanche: 0
Avg avalanche: 0
0 grains
1 grain
2 grains
3 grains
Toppling
Power-law avalanches: P(s) ~ s^(-3/2). Self-organized criticality without tuning.