Rock weathering plays a crucial role in landscape evolution and is observed worldwide. In arid regions, salt weathering is a key mechanism driving rock disintegration and is commonly linked to the expansion and contraction of salts during repeated cycles of salt dissolution and recrystallization. However, the environmental conditions governing such moisture fluctuations, in hyperarid environments where moisture availability is limited, remain poorly understood.
This study presents new findings that quantify the microclimatic conditions associated with salt-driven crack propagation processes within gravels in natural hyperarid settings using acoustic emission (AE) measurements. The AE measurements were carried out for seven salt-laden cracked boulders perched on abandoned shorelines of the hypersaline Dead Sea between April 2023 and January 2025. Continuous measurements of environmental conditions, e.g., air temperature (T) and relative humidity (RH) were also acquired during this time frame. Our results revealed a bimodal pattern of micro-fracturing activity, with AE activity peaks concentrated either in the early morning or late afternoon hours. This timing of AE peaks appears to be associated with the diurnal maximum or minimum in atmospheric RH fluctuations, respectively.
Time-lapse imagery also revealed a recurring pattern of salt crystallization along rock cracks during afternoon hours with minimum RH values, followed by the disappearance of salt crystals by dissolution (deliquescence) after the morning RH peak. The formation of salt crystals during the driest, warmest hours and their dissolution during the coldest, most humid hours suggest that stress induced by repeated salt deliquescence/efflorescence cycles is likely responsible for the observed pattern in fracturing activity.
The process of cyclic salt deliquescence/efflorescence requires moisture sources, which are minimal in hyperarid settings. Our results provide unprecedented quantitative evidence for the important role that RH can play in salt weathering in hyperarid environments. Diurnal and seasonal atmospheric RH fluctuations result in volumetric changes of hygroscopic salts minerals likely have a significant role in progressive rock fracturing in extremely dry salt-rich environments. This weathering mechanism could be relevant not only on Earth but also on Mars, where other moisture sources are absent.