Effect of Earth-Air Movement on Water Transport in the Rock Surrounding Cave B113 in the Mogao Grottoes

Abstract

The degradation of wall paintings in the Mogao Grottoes, China, is primarily caused by the migration of water and salt in the surrounding rock (SR), with water being the key influencing factor. However, it remains unclear whether the movement of earth-air, driven by the air pressure difference (APD) between the air inside the SR and the external atmospheric pressure (AP), affects water transport in the rock. This study focuses on Cave B113 to investigate the effect of earth-air movement on water transport in the cave's SR. Under closed conditions, the APD was monitored at depths of 10, 20, and 30 cm within the SR. The results indicate that when the AP changes, the APD fluctuates in the opposite direction and increases with depth in the SR. The Pearson correlation coefficients between the AP and APD at depths of 20 and 30 cm are −0.31 and −0.32, respectively. The APD reflects the influence of AP on the SR and serves as a driving force that directly governs the movement of earth-air. The concentration of the water vapour in the SR layers is affected by temperature, while the relative and absolute humidities of these layers are influenced by the ascending and descending movement of earth-air. The magnitude of the AP fluctuation determines the volume of water that migrates inside the SR. Collectively, these factors determine the amount of evaporation that occurs and the characteristics of the moisture present in the rock surrounding the cave. This study elucidates the pivotal factors contributing to the deterioration of the wall paintings in the cave, providing a scientific basis for developing new ways of protecting these wall paintings. It has extensive reference value for water transport and evaporation in the vadose zone.