Surface fluctuations in a slowly driven granular system

We report an experiment on a granular packing: a box filled with glass beads is tilted very slowly up to the maximum angle of stability where a big avalanche is produced. During the build-up period many rearrangements occur on the free surface of the packing. Digital imaging was used to study these rearrangements. The probability distribution of sizes for the observed mass fluctuations follow a power-law behavior, which is the signature of self-organized criticality. However, this description breaks down in the limit of big rearrangements where inertia effects are not negligible.