Open the Sandpile model from the Chemistry and Physics section of the NetLogo models library. This model, originally developed by Bak, Teng, and Weisenfeld (1987), was the first model in which self-organizing criticality was presented. The white flashes help you distinguish successive avalanches. They also give you an idea of how big each avalanche was. Most avalanches are small. Occasionally a much larger one happens. Describe how it is possible that adding one grain of sand at a time can cause so many squares to be affected. Can you predict when a big avalanche is about to happen? What do you look for?