Quantifying frost-weathering-induced damage in alpine rocks

Abstract

Frost weathering is a key mechanism of rock failure in periglacial environments and landscape evolution. In high-alpine rock walls, freezing regimes are a combination of diurnal and sustained seasonal freeze–thaw regimes, and both influence frost cracking processes. Recent studies have tested the effectiveness of freeze–thaw cycles by measuring weathering proxies for frost damage in low-strength and in grain-supported pore space rocks, but detecting frost damage in low-porosity and crack-dominated alpine rocks is challenging due to small changes in these proxies that are close to the detection limit. Consequently, the assessment of frost weathering efficacy in alpine rocks may be flawed. In order to fully determine the effectiveness of both freezing regimes, freeze–thaw cycles and sustained freezing were simulated on low-porosity, high-strength Dachstein limestone with varying saturation. Frost-induced rock damage was uniquely quantified by combining X-ray computed microtomography (µCT), acoustic emission (AE) monitoring, and frost cracking modelling. To differentiate between potential mechanisms of rock damage, thermal- and ice-induced stresses were simulated and compared to AE activity. Our results underscore the significant impact of initial crack density on frost damage, with µCT scans revealing damage primarily through crack expansion. Discrepancies between AE signals and visible damage indicate the complexity of damage mechanisms. The study highlights frost cracking as the main driver of rock damage during freezing periods. Notably, damage is more severe during repeated freeze–thaw cycles compared to extended periods of freezing, a finding that diverges from field studies. This discrepancy could stem from limited water mobility due to low porosity or from the short duration of our experimental setup.