Abstract
We present two simple experiments on granular flow. Though the notion of pile angle is common, it appears that there can be many different angles depending on the experiment \cite{wieghardt,herrmann}. Our first experiment also shows, in a conical geometry, that the dynamics of the flow leading to these angles depends strongly on the density of the pile and presumably on its internal structure, in contrast (surprisingly) to the final profile. Our second experiment studies the hysteresis between the static and dynamical angle in the case of a thin layer of beads on a rough inclined plane. Between these two angles, an avalanche is amplified while going down, and we observe that it grows lateraly leaving a triangular track, whose opening angle increases as the plane inclination approaches the static angle. Before reaching this limit, the avalanche starts to propagate upwards.