How do canyon-shaped cave passages form?

Canyon-shaped cave passages form when a cave transitions from pipe flow to open-channel flow. Initially, when a conduit is completely filled with water, dissolution occurs uniformly across the walls, ceiling, and floor, creating an elliptical or circular tube.12

As the water source becomes limited, a free air surface develops within the passage. Once this transition occurs, dissolution of the ceiling ceases, and the water acts only upon the bed of the stream. Continued solutional erosion causes the passage to deepen, resulting in a narrow, canyon-like shape. These passages can become quite extreme in proportion; in some instances, they may reach heights of 30 to 50 metres while remaining only one metre or less in width. The resulting shape is often influenced by the meandering of the downcutting stream, which can create irregular wall patterns.12