  We investigate the impact of a free-falling water drop onto a granular layer.
First, we constructed a phase diagram of crater shapes with two control
parameters, impact speed and grain size. A low-speed impact makes a deeper
cylindrical crater in a fluffy granular target. After high-speed impacts, we
observed a convex bump higher than the initial surface level instead of a
crater. The inner ring can be also observed in medium impact speed regime.
Quantitatively, we found a scaling law for crater radius with a dimensionless
number consisting of impact speed and density ratio between the bulk granular
layer and water drop. This scaling demonstrates that the water drop deformation
is crucial to understand the crater morphology.
