Order and disorder in columnar joints
Seminar Room 1, Newton Institute
Columnar joints are three-dimensional fracture networks that form in cooling basaltic lava flows. The network organizes the solid flow into ordered, mostly hexagonal columns. Famous examples include the Giant's Causeway in Northern Ireland and Fingal's cave in Scotland. The same pattern can be observed on a smaller scale in desiccating corn starch, and in some other materials. We have made the first three dimensional study of the evolution of the network in corn starch and relate these observations to the mature patterns observed in basalt. The starch patterns are statistically similar to those found in the Giant's Causeway, suggesting that mature columnar joint patterns contain inherent residual disorder. We find that the starch patterns can be made more similar to the basaltic ones using controlled drying rate conditions. Discontinuous transitions in pattern scale can be observed under constant external drying conditions, which may prompt a reinterpretation of similar transitions found in basalt. We also made some field observations of basalts in the Columbia river formation in Washington State, and observed a possible secondary instability of the mature columnar pattern.