Pumice-pumice collisions and the effect of the impact angle

[1] Using a high-speed video camera, we studied oblique collisions of lapilli-size pumice cylinders (with no rotation before impact) on flat pumice targets. Our results show that the rebound angle, the ratios of the components of velocities and the energy loss vary with the impact angle. In particular, in collisions with an average yaw angle approximately equal to zero, we observed relatively larger rebound angles at small and large impact angles and smaller values in between (the angles are measured from the horizontal surfaces of the targets). We observed also that the ratio of the normal components of velocities decreases and the ratio of the horizontal components increases when the impact angle increases. Furthermore, the ratio of the kinetic energy after to that before collisions, in general, decreases when the impact angle increases. Thus, our experiments reveal features that could be useful in modelling pumice-pumice collisions in geophysical flows.