The Bak-Tang-Wiesenfeld forest fire model: trees grow slowly, lightning strikes ignite fires that spread via nearest neighbors. The system self-organizes to a critical state with power-law fire size distributions — P(s) ~ s^{−τ}.
SOC (Bak, Tang, Wiesenfeld 1990): the forest fire is a slow-driven, dissipative system that reaches criticality without parameter tuning. The ratio p/f controls the average cluster size before lightning. At criticality the fire-size distribution is a power law with exponent τ ≈ 1.19 in 2D. Large fires are rare but inevitable — no characteristic scale exists.