Experimental Investigation of Moisture Movement During Freeze–Thaw Cycles and Its Effect on Physical Rock Weathering in Low-Porosity Alpine Limestone

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Mitchell, Andrew ; Sass, Oliver:
Experimental Investigation of Moisture Movement During Freeze–Thaw Cycles and Its Effect on Physical Rock Weathering in Low-Porosity Alpine Limestone.
In: Permafrost and Periglacial Processes. Bd. 37 (2026) Heft 3 . - S. 354-371.
ISSN 1099-1530
DOI der Verlagsversion: https://doi.org/10.1002/ppp.70035

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Abstract

The progressive weakening of alpine rockwalls through subcritical cracking, driven by repeated low-magnitude stress processes, plays a key role in alpine rock weathering. Laboratory studies using acoustic emission (AE) monitoring have shown that thermal stresses from freeze–thaw cycling induce crack propagation, with recent work highlighting the influence of rock moisture saturation. However, the role of moisture availability and movement within the outer rockwall remains poorly constrained. To address this gap, we conducted laboratory experiments on 40 × 20 × 20 cm samples of Wetterstein limestone (Northern Calcareous Alps), using AE sensors to track subcritical cracking during repeated diurnal and 72-h freeze–thaw cycles between 7°C and −8°C. Initial rock moisture saturation was varied across runs, and moisture redistribution was monitored via electrical resistance measurements. Our results show that while higher saturation generally enhances rock weathering, maximum crack intensity occurs at 70%–75% saturation, challenging the assumption that > 91% saturation represents optimal conditions. Among moisture-driven processes, volumetric expansion produced the highest weathering intensities (but for a shorter period of time), whereas ice segregation generated greater cumulative subcritical cracking due to the longer duration. Based on these findings and evidence of ice segregation, we propose a refined frost cracking window of −4°C to −9°C for Wetterstein limestone. These insights advance our understanding of the coupled role of rock moisture and temperature in alpine rockwall preconditioning for rockfall, though further work is needed to assess the impact of wet-dry weathering during freeze–thaw cycles and the role of increased surface moisture availability.