Salt-weathering simulations under hot desert conditions: agents of enlightenment or perpetuators of preconceptions?

Because of access difficulties and inhospitable environmental conditions, our understanding of rock weathering in hot deserts has been strongly influenced by laboratory simulations. However, a risk exists that results may come to owe more to experimental design than to actual environmental conditions experienced at the atmosphere/rock surface interface. This was especially true in early salt-weathering simulations that seemingly sought to reinforce the orthodoxy of a physically dominated weathering environment driven by extremely high absolute temperatures and large diurnal temperature ranges. However, improvements in environmental sensors over the last 20 years have established the complexity of desert climates and the importance of microclimatic controls and allowed considerable refinement of experimental design. This overview evaluates the implications of recent simulation studies and presents new information on possible fatigue effects of differential thermal expansion of salts and the salt weathering of test blocks under compressive loading. In doing so, it demonstrates how physical rock properties change during experimentation, the importance of short-term surface temperature fluctuations, distinctions between the weathering of unconfined debris and larger rock surfaces, the importance of moisture and salt applications that replicate their availability in deserts, the importance of rock thermal properties in controlling their weathering response in environments dominated by radiative heating and cooling, and the overall complexity of weathering regimes.