Figure 3.

Surface growth of a narwhal tusk with an upward pointing material velocity, V = V^Г + V^g, according to equation (16). Photograph of a narwhal tusk, left, demonstrates the characteristic helical growth pattern. Computational simulation of surface growth, right, with an outward pointing velocity V^Г of the growth surface Г, here characterized through the bottom ring, and a helically upward pointing velocity V^g of material grown at the surface Г.