slow motion : crater formation by drop impacts on sand

We have studied the splashing dynamics of water drops impacting granular layers. Depending on the drop kinetic energy, various shapes are observed for the resulting craters. Experimental parameters that have been considered are : the size of the millimetric droplets; the height of the free fall, ranging from 1.5 cm to 100 cm; and the diameter of the grains. As the drop is impacting the granular layer, energy is dissipated and a splash of grain occurs. Meanwhile, surface tension, inertia and viscosity compete, leading to strong deformations of the drop which depend on the experimental conditions. Just after the drop enters into contact with the granular bed, imbibition takes place and increases the apparent viscosity of the fluid. The drop motion is stopped by this phenomenon. Images and fast-video recordings of the impacts allowed to find scaling laws for the crater morphology and size.
This abstract is related to a fluid dynamics video for the APS DFD gallery of fluid motion 2010.