Karst Conduit Breakthrough

A narrow fracture in limestone widens as CO₂-charged groundwater dissolves its walls, but the process is anything but steady. This simulation couples cubic-law fracture flow to Plummer–Wigley–Parkhurst dissolution kinetics — including the real "kinetic trigger" that sharply slows reaction rates near chemical saturation — and integrates the resulting mass balance to grow the fracture's aperture over simulated centuries and millennia. Early on the fracture is so narrow that percolating water saturates within millimetres and dissolution nearly stalls; as the opening creeps wider, faster flow keeps water undersaturated for longer, which dissolves rock faster still, in a runaway feedback loop that ends in a sudden "breakthrough" into a fast, turbulent cave passage — the mechanism geologists credit for why karst conduits form after long incubation periods rather than growing at a constant rate.