Self-organization, the cascade model and natural hazards.

We consider the frequncy-size statistics of two natural hazards, forest fires and landslides. Both appear to satisfy power-law (fractal) distributios to a good approximation under a wide variety of condition. Two simple cellular-automata models have been proposed as analogs for this observed behavior, the forest fire model for forest fires and the sand pile model for landslides. The behavior of these models can been understood in terms of a self-similar inverse cascade. For the forest fire model the cascade consists of the coalescence of clusters of trees; for the sand pile model the cascade consists of the coalescence of the metastable regions.