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

Abstract

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.

Thermoelasticity of ice explains widespread damage in dripstone caves during glacial periods

“…Permafrost was widespread in the Central Europe between the southern margin of the Scandinavian ice sheet and the Alpine ice sheet, including the southern part of England 20 . It is therefore not surprising that most reports of presumably ice-damaged speleothems are from caves extending from Slovakia 16 and the Czech Republic 17 to Germany 14 , 33 – 35 , Belgium 36 and southern England 15 . No systematic dating of damaged stalagmites at these sites has been performed, but the 230 Th ages of the associated CCC range mostly from about 40 to 15 ka 37 – 40 , demonstrating the presence of ice in these (currently ice-free) caves.…”

Pleistocene speleothem fracturing in the foreland of the Western Carpathians: a case study from the seismically active eastern margin of the Bohemian Massif

“…How ever, the same speleothem frac tur ing from the same cave was in ter preted as tec tonic in or i gin in an ex haus tive re view by Šebela (2008). The depth of ice for ma tion in caves is usu ally de pend ent on per ma frost depths (Kempe, 2004;Žák et al, 2011) but a steady flow of cold (-10 to -15°) air dur ing win ter sea sons in periglacial ar eas can cause the freezing of cave floor sed i ments and flowstone frac tur ing, even without sig nif i cant ice for ma tion (Lundberg and McFarlane, 2012). Cryo genic cave car bon ates (CCC) have in deed been described from the shal low-subsurface parts (<30 m) of the Javoříčko Cave (Žák et al, 2011).…”

“…In ad di tion to past earth quakes, even the pres ent-day fault dis place ment and speleo them de struc tion can be mon i tored in real time us ing exten som eters (Kashima, 1993;Gilli, 2005;Briestenský et al, 2010). On the other hand, there is on go ing de bate about the aseismic causes of speleothem break age, such as the hu man pres ence in caves, shocks due to mine blast ing, cryo genic fractur ing, grav i ta tional col lapse, and cat a strophic floods (Crispim, 1999;Gilli, 2005;Frumkin et al, 2009;Becker et al, 2012;Lundberg and McFarlane, 2012). De spite the con tro versy, it is some times pos si ble to elim i nate aseismic frac tur ing by care ful ob ser va tion of speleothem mor phol ogy and ac com pa ny ing ev idence such as the study of soda-straws, which are re garded as re li able in di ca tors of co-seis mic frac tur ing Becker et al, 2006), and/or by se lect ing caves un touched by past hu man ac tiv ity.…”

Permafrost occurrence during the Last Permafrost Maximum in the Western Carpathian Mountains of Slovakia as inferred from cryogenic cave carbonate

“…The nature of the morphologic indicators of permafrost in caves has been discussed by Kempe et al . (), Lundberg & McFarlane () and Orvošová et al . () and is not covered in detail here.…”