Cryogenic fracturing of calcite flowstone in caves: theoretical considerations and field observations in Kents Cavern, Devon, UK

Several caves in Devon, England, have been noted for extensive cracking of substantial flowstone floors. Conjectural explanations have included earthquake damage, local shock damage from collapsing cave passages, hydraulic pressure, and cryogenic processes. Here we present a theoretical model to demonstrate that frost-heaving and fracture of flowstone floors that overlie wet sediments is both a feasible and likely consequence of unidirectional air flow or cold-air ponding in caves, and argue that this is the most likely mechanism for flowstone cracking in caves located in Pleistocene periglacial environments outside of tectonically active regions. Modeled parameters for a main passage in Kents Cavern, Devon, demonstrate that 1 to 6 months of -10 to -15° C air flow at very modest velocities will result in freezing of 1 to 3 m of saturated sediment fill. The resultant frost heave increases with passage width and depth of frozen sediments. In the most conservative estimate, freezing over one winter season of 2 m of sediment in a 6-m wide passage could fracture flowstone floors up to ~13 cm thick, rising to ~23 cm in a 12-m wide passage. Natural flaws in the flowstone increase the thickness that could be shattered. These numbers are quite consistent with the field evidence.