Spacetime diagram of two 3D runs with particle size τ_f = 0.03 and Δ = 0.05. The color indicates the column density Σ_solid/ ⟨ Σ_solid ⟩ using the same color bar as Figs. 4 and 5. Both runs begin with Z = 0.01 and have Z increased only for a short interval. In one run (left), Z grows to 0.02 and in the other (right) Z grows to 0.03. Clumps are visible for Z ≥ 0.02, consistent with the 2D runs.