  Sudden release of energy in explosion creates craters in granular media. In
comparison with well-studied impact cratering in granular media, our
understanding of explosion cratering is still primitive. Here, we study
low-energy lab-scale explosion cratering in 3D granular media using controlled
pulses of pressurized air. We identify four regimes of explosion cratering at
different burial depths, which are associated with distinct explosion dynamics
and result in different crater morphologies. We propose a general relation
between the dynamics of granular flows and the surface structures of resulting
craters. Moreover, we measure the diameter of explosion craters as a function
of explosion pressures, durations and burial depths. We find that the size of
craters is non-monotonic with increasing burial depths, reaching a maximum at
an intermediate burial depth. In addition, the crater diameter shows a weak
dependence on explosion pressures and durations at small burial depths. We
construct a simple model to explain this finding. Finally, we explore the
scaling relations of the size of explosion craters. Despite the huge difference
in energy scales, we find that the diameter of explosion craters in our
experiments follows the same cube root energy scaling as explosion cratering at
high energies. We also discuss the dependence of rescaled crater sizes on the
inertial numbers of granular flows. These results shed light onto the rich
dynamics of 3D explosion cratering and provide new insights into the general
physical principles governing granular cratering processes.
