Slippery Slopes and the Angle of Repose

Have you ever seen an avalanche or landslide roll down a hill? Why is it that at one moment, everything seems fine, then suddenly the mountain begins to slump? It has something to do with how the earth or snow is piled up on the mountain. Generally, granular materials such as snow or earth pile up relatively well. However, if the slope angle gets too steep, the materials will start to slide down the slope. This critical slope angle, also called the angle of repose, is different for different materials. In this activity, you will create your own little avalanches and determine the angle of repose for different materials along the way!