Illustration of the effect of the shell curvature on the formation of clumps and pillars. Density cut and velocity field (for the unionized gas) are taken from the simulations of Paper I. Initial curvature radius: left 5 × 10^-2 pc and right 1 × 10^-2 pc. Top: 20 ky after the beginning of the simulation, the shell is formed on the curved surface. Bottom: snapshots after 550 ky. A 1.5-pc long pillar is formed at high curvature, whereas a clump of the size of the initial structure is formed at low curvature.