Modelling the evolution of columnar joints

摘要: Abstract Cooling cracks, developing from the margins of solidifying lava flows or intrusive dykes sills, often propagate inward and divide rock into prismatic columns. It has been shown that: (1) initial crack pattern that forms at surface body is not as regular pseudo-hexagonal which evolves later; (2) columnar structures develop by repeated, step-wise advances, forming cm to dm transverse bands on column faces; (3) even within well-developed colonnades, polygonal outlines continue shift slightly one advance next. We propose each new should parallel highest thermal gradient ahead current tip. When adjacent columns are unequal size, local asymmetry isotherms drives toward biggest hottest column. present a geometrical model algorithm follows this rule mimics successive advances cooling front migrates sheet, dyke. The obtained consists convex, irregular polygons with variable number sides, but in pentagons hexagons predominate. successfully reproduces rapid evolution an initial, immature pseudo-hexagonal, mature average sides approaches six. predicts also predominance Y -type junctions, approximately equal sizes, persistent changes length diverging orientation growth steps observed along patterns exhibit properties very similar those jointed such Giant's Causeway.