Why can a cave passage become dry after an underground stream cuts to a lower level?

A cave passage becomes dry when the underground stream that formed it is diverted to a lower level. This process is closely linked to the evolution of the surrounding landscape and the water table.1

As surface streams downcut their beds over time, the base level and the water table are lowered. During this period, insoluble sediments often accumulate on the floors of existing cave conduits, which helps protect the bedrock from further solutional erosion.1

As the surface streams continue to lower the landscape, the increased hydraulic gradient encourages the formation of new, more efficient passages at lower elevations. Eventually, the underground flow is completely diverted into these new, lower-level conduits. Consequently, the original, higher-level passages are abandoned by the water, leaving them air-filled and dry above the descending water table. These abandoned segments may then enter a stage of stagnation, where they can persist for millions of years.123