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

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.

A microdestructive method using dye-coated-probe to visualize capillary, diffusion and evaporation zones in porous materials.

The vaporization plane, a narrow zone of subsurface evaporation often present in porous rocks, separates the region where water flows due to capillary forces from the dry zone where moisture moves in gas phase only. The knowledge of its depth and geometry is critical for estimating water flux in rock-atmosphere interphase, for understanding moisture distribution and for localization of damaging salt crystallization. Yet, an easy-to-use method applicable in the exterior has been missing. This strongly limits interpretation of moisture-related measurements as moisture content differences in the above-mentioned zones are often immeasurable by currently used field techniques. We have introduced a new micro-destructive method to measure the vaporization plane depth using an instrument consisting of a rod, adhesive, and dye powder, reacting with moisture, that is inserted into porous materials in 2 mm diameter holes. We tested different rods, adhesives, and dyes, and the best combination of these has been used in >500 experiments to determine the vaporization plane depth in porous rocks and building materials. The knowledge of vaporization plane depth enables more reliably to interpret the moisture and suction data obtained from numerous existing techniques. This new uranine-probe method should be thus of interest to many scientific disciplines: evaporation, unsaturated hydrology, weathering, or geobiology.