Evaporation rate from surfaces of various granular rocks: Comparison of measured and calculated values

Abstract

Knowledge of the evaporation rate from rock surfaces is critical for obtaining the water flux in the rock-atmosphere interphase, for understanding moisture distribution, and for quantification of damage from salt crystallization within the rock. Evaporation from rocks is a poorly understood, yet important process. We present a study on evaporation from 10 lithologies, including sedimentary, igneous, and metamorphic granular rocks. The evaporation rate was measured from rock cores with a set vaporization plane depth in a humid temperate continental climate during at least eight observation periods for eight months. The measured evaporation rate varied over four orders of magnitude (0.4-2447 mm/year), being dependent on the vaporization plane depth, lithology, and climate seasonality at the site. The evaporation rate from the rock cores was calculated based on Fick's law. The calculations reasonably followed the measured values. Using contrasting, yet field-realistic values in the calculation, virtual time series of the seasonal evaporation rate from natural rock outcrops in three different climates (arid, semi-arid, humid) were constructed. This revealed possible annual evaporative losses from the rock outcrops (0.1 mm-896 mm). Within the range of observed values, the evaporation rate was mostly influenced by the vaporization plane depth (by up to 2.2 orders of magnitude), which was followed by: lithology (up to 1.1 order of magnitude), local climate (up to 1.0 order of magnitude), and climate seasonality (up to 0.8 order of magnitude). Thus, our study shows the key role of the vaporization plane depth in the evaporation rate. This approach can find employment in a large number of investigations such as in the evaporation estimates and hydrologic balance in rock landforms and rocky slopes, hydrologic processes in the shallow rock subsurface, living conditions of endolithic and epilithic organisms, weathering processes, and in the protection of carved or rock constructed cultural heritage.

Keywords: Diffusion; Evaporation front; Hydrologic balance; Vaporization plane; Weathering.