Abstract

Natural sculpting processes such as erosion or dissolution often yield universal shapes that bear no imprint or memory of the initial conditions. I will present the results of laboratory experiments aimed at assessing the shape dynamics for the simple case of a dissolvable boundary immersed in a fluid. Though no external flow is imposed, dissolution and consequent density differences lead to buoyancy-driven flows that in turn strongly affect local dissolving rates and shape changes, and we identify two distinct behaviours. A flat boundary dissolving from its lower surface tends to retain its overall shape while developing small-scale roughness that reflects complex near-body flows. A boundary dissolving from its upper surface tends to erase its initial shape and form an upward spike structure that sharpens indefinitely. We propose an explanation for these different outcomes based on observations of the coupled shape dynamics, concentration fields, and flows.