Why do cave roofs collapse as passages become wider?

Cave roofs are constantly under stress, as the weight of the ceiling beds causes them to sag and separate along weaker bedding planes. Each ceiling bed functions as a fixed beam spanning the width of the passage, and there is a strict mechanical relationship between the beam's thickness, its density, and the width of that span.1

When a passage widens, the span of these ceiling beams increases. Once the width exceeds a critical value, the ceiling can no longer support its own weight and collapses. This process is often exacerbated by solution along vertical joints, which cuts the ceiling beams and turns them into cantilevers with significantly lower critical load capacities. Furthermore, when one ceiling bed falls, it removes support from the bed above it, which may then also collapse in a process known as upward stoping.1