At a temperature below 100 K on Mg(0001), a variety of further diffusion processes become active such as dimer and trimer propagation, diffusion along an edge, the formation of 60° and 120° corners, switching sides at 240° and 300° corners and kink incorporation. Especially the activated corner-crossing barriers contribute to the growth of compact rather than fractal islands. Interestingly, both the dimer step-down and step-up processes become possible in this temperature range, contrary to uniform and smooth surface growth.