Impact cratering begins with contact and compression, in which a shock rapidly heats and compresses target and impactor. During excavation, material moves outward and upward, producing a transient cavity and ejecta. Modification then involves gravitational collapse, wall slumping, fallback and, for large structures, rebound and central features. The stages overlap in time; crater size and morphology depend on gravity, impact conditions and target strength, not just the projectile's geometric hole size.
