Experimental observations that simulated active-layer deepening drives deeper rock fracture

• Published in: Permafrost and Periglacial Processes
• Main Authors: Maji, Vikram, Murton, Julian B
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: QE0001 General Including geographical divisions; Permafrost and Periglacial Processes
• Online Access: http://sro.sussex.ac.uk/id/eprint/89351/; http://sro.sussex.ac.uk/id/eprint/89351/1/Accepted%20ms%20PPP.pdf; https://doi.org/10.1002/ppp.2041

The impact of changes in active-layer thickness on the depth of pervasive macrofracture (brecciation) in frost-susceptible bedrock is unclear but important to understanding its physical properties and geohazard potential. Here we report results from a laboratory experiment to test the hypothesis that active-layer deepening drives an increase in the depth of brecciation. The experiment simulated active-layer deepening in 300 mm cubic blocks of limestone (chalk) and sandstone. Temperature, surface heave and strain at depth were measured during 16 freeze–thaw cycles. Macrocracks photographed at intervals were digitally analysed to visualise crack growth and to quantify crack inclination and length. In chalk, an upper horizon of macrocracks developed first at about 100 mm depth in a shallow thaw active layer during cycles 1–8, followed by a lower horizon at about 175‒225 mm depth in a deeper thaw active layer during cycles 9–16. The longest cracks (>35 mm) were most common at inclinations of 0–30° from horizontal, and numerous cracks <5 to 15 mm long developed at inclinations of 40–50°, with some longer vertical to subvertical cracks linking the two brecciated horizons. Overall, the observations support the hypothesis that a thickening active layer drives deeper rock fracture by ice segregation.