Prisms generated by joints in experiments of water-starch mixture

Abstract

We present a didactic experiment of desiccation using starch-water mixture. The aim is to obtain prismatic joints similar to columns in basalt lava flows, or the desiccation fractures in sediments. Two types of joints were observed in experiments: a) the first formed joints are large, crossing completely the container used in the experiment. The intersection angles among the large joints are about 90°; b) The second joints are smaller; they develop after the large ones forming intersection angles from 90° to 140°. Both large and small joints have dips near 90° with respect the dissection surface. Using Voronoi diagrams we explained patterns which resemble the prismatic joints obtained in the experiment.