Order and disorder in columnar joints

Lucas Goehring and S. W. Morris

Department of Physics, University of Toronto,

60 St. George St., Toronto, Ontario, Canada M5S 1A7.

Europhys. Lett. 69, 739-744 (2005)

Download preprint pdf: GM05.pdf

Columnar joints are three-dimensional fracture networks that form in cooling basalt and several other media.  The network organizes itself into ordered, mostly hexagonal columns. The same pattern can be observed on a smaller scale in desiccating starch. We show how surface boundary conditions in the desiccation of starch affect the formation of columnar joints.  Under constant drying power conditions, we find a power law dependence of columnar cross-sectional area with depth, while under constant drying rate conditions this coarsening is eventually halted. Discontinuous transitions in pattern scale can be observed under constant external conditions, which may prompt a reinterpretation of similar transitions found in basalt. Starch patterns are

statistically similar to those found in basalt, suggesting that mature columnar jointing patterns contain inherent residual disorder, but are statistically scale invariant.