Rock weathering : The effects of varying rock moisture on controlled weathering cycles in low porosity limestone

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Mitchell, Andrew ; Sass, Oliver:
Rock weathering : The effects of varying rock moisture on controlled weathering cycles in low porosity limestone.
In: Geomorphology. Bd. 457 (2024) . - 109149.
ISSN 0169-555x
DOI: https://doi.org/10.1016/j.geomorph.2024.109149

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Abstract

Examples of rockwall weathering processes include diurnal heating and cooling, diurnal and seasonal freezing, wetting and drying and thawing/seasonal active-layer thawing. These stress-loading processes often occur synergistically and cause a weakening of the rockwall through the propagation of sub-critical cracks. The Acoustic Emissions (AE) released by these cracking events can be measured in order to quantify the weathering efficacy. While the effects of thermal cycling are well studied, rock moisture content and its control on these weathering processes is rarely considered in detail.

To better understand rock moistures effect on weathering processes we subjected Wetterstein limestone samples with different starting moisture contents (0 %, 25 %, 50 %, 75 %, 100 %) to thermal cycling above (5 to 35 °C) and below (5 to −10 °C) freezing and a longer freezing cycle with gradual stepped thawing (10 to −10 °C). In addition to this we simulated wetting and drying cycles at a constant temperature. For all of these weathering cycles, relative efficacy was assessed by amount of AE hits and change in effective porosity.

Rock moisture was found to have little effect on the overall AE count and effective porosity increase over shorter thermal cycling. However, freeze-thaw cycling was shown to have similar weathering effect to thermal cycling of 3 K greater thermal gradient above freezing. Meanwhile longer duration freezing cycles see an increase of rock moisture create 4× as many cracking events compared to dry samples. More re-freezing events are seen in lower saturation samples and when considered with the synergistic effects of wetting and drying in natural open systems, the presence and mobility of pore water are considered to be more important than the quantity.