Anomalous transport in conical granular piles

Experiments on $2+1$-dimensional piles of elongated particles are performed. Comparison with previous experiments in $1+1$ dimensions shows that the addition of one extra dimension to the dynamics changes completely the avalanche properties, with the appearance of a characteristic avalanche size. Nevertheless, the time which single grains need to cross the whole pile varies smoothly between several orders of magnitude, from a few seconds to more than 100 hours. This behavior is described by a power-law distribution, signaling the existence of scale invariance in the transport process.