Impact cratering by pi-group scaling: energy, transient and final crater size, and a growing cross-section.
The science
The impactor carries kinetic energy E = 1/2 m v^2 with m = rho_i pi L^3 / 6; one megaton of TNT is 4.184e15 J. Crater size follows the pi-group scaling of Collins, Melosh and Marcus (2005): the transient crater diameter is D_tc = 1.161 (rho_i/rho_t)^(1/3) L^0.78 v^0.44 g^(-0.22) sin(theta)^(1/3) (SI units).
Small craters collapse to a bowl: D_final = 1.25 D_tc with depth about D/5. Beyond about 3.2 km on Earth the crater collapses into a complex crater, D_final = 1.17 D_tc^1.13 / D_sc^0.13, which is shallower; the depth law shown for complex craters is only indicative. The animation is a schematic of excavation, rim uplift and collapse, not a hydrocode.
Simplifications: no atmospheric entry beyond a rule-of-thumb survival limit (about 20 m iron, 50 m stone, 150 m ice), a non-porous target, flat ground, the Earth gravity only. The benchmark checks (Barringer crater and the 1908 Tunguska energy) show the typical tolerance: a factor 1.3 on diameter and a factor 2 on energy.