Crater formation during raindrop impact on sand

TL;DR

This study investigates how raindrop impacts create craters in sand, revealing the roles of impact velocity, packing density, and grain avalanches in shaping the crater's transient and final forms.

Contribution

It introduces a model linking impact energy to crater dimensions and examines how packing density influences crater evolution and aspect ratio.

Findings

Crater diameter scales with impact energy across packing densities.

Avalanches significantly influence the final crater shape.

Transient crater aspect ratio varies with packing fraction.

Abstract

After a raindrop impacts on a granular bed, a crater is formed as both drop and target deform. After an initial, transient, phase in which the maximum crater depth is reached, the crater broadens outwards until a final steady shape is attained. By varying the impact velocity of the drop and the packing density of the bed, we find that avalanches of grains are important in the second phase and hence, affect the final crater shape. In a previous paper, we introduced an estimate of the impact energy going solely into sand deformation and here we show that both the transient and final crater diameter collapse with this quantity for various packing densities. The aspect ratio of the transient crater is however altered by changes in the packing fraction.