Abstract

Climatically induced cycles of stone temperature and moisture content may result in physical rock weathering through various mechanisms. These mechanisms cause rock to oscillate between periods of expansion and contraction, resulting in compressive and tensile stresses. Cycles of compression and tension may cause fatigue of the stone and therefore the frequency of these cycles may be of critical importance. The temperature and moisture content of stones with four different aspects were monitored over one year and the frequency of heating-cooling, wetting-drying and freeze-thaw cycles calculated. Heating-cooling cycles were found to occur on all aspects, but the highest frequency of cycles occurred on south and west aspects during summer months. Heating and cooling of stone creates a thermal gradient within the stone, which is critical in causing insolation weathering. Differences in the rate of thermal expansion between minerals or superficially degraded parts of stone may also contribute to breakdown. Moisture availability may alter the mechanisms by which heating—cooling causes weathering. Cycles of wetting—drying are less frequent than heating—cooling cycles, but may cause weathering by five mechanisms, depending upon the hygrometric gradients. Freeze-thaw cycles show a much lower frequency than heating—cooling and wetting—drying cycles, but are active on all aspects.

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