The natural environment in which the caves are located is very complicated. During this period, various scientific approaches were undertaken to understand the characteristics of the grotto sites, the natural environment
In which they are found, and the relationship between these factors. Studies were also conducted on the deterioration of and causes of damage to statues and wall paintings in the grottoes.
Approaches to environmental monitoring
The present conditions of the caves, sculptures, and murals inside the caves are complex, and their management and protection are affected by environmental factors. Several scientific approaches were taken to monitor the cave relics and their natural environment from diverse aspects, as follows:
Weather monitoring. A fully automated weather station was installed above the Mogao caves to measure temperature, humidity, ground-surface temperature, wind direction, wind speed, sunlight, and precipitation. Accurate data collected over four years reveal the basic characteristics of weather patterns and provide scientific data for studying the microenvironment and the causes of deterioration inside the caves (Li and Zhang 1993; Miura 1993).
Microenvironmental monitoring. Caves of different sizes, different depths, different levels, with and without doors, and open or restricted to visitors were selected for long - and short-term monitoring of the microenvironment inside the caves using fully or semiautomated equipment. The data obtained provided scientific evidence for the study of the preservation of murals and sculptures, causes of deterioration, the effects of visitors on the caves, and the study of the optimum environment in the caves (Zhang and Wang 1993).
Hydrogeology. Systematic analyses were carried out on the chemical components of the ground-surface water from the Daquan River and on the cliff rock of the Mogao caves. Results show that the ground-surface water has a high content of soluble salts. Dampness in the caves on the lower level was found to be brought about by the capillary movement of irrigation water that permeated into the lower levels of the caves and damaged the paintings. Studies also showed that the precipitation that infiltrates downward into the upper layer of the Mogao caves, along with the pressure exerted by the overlying rock, led to the delamination and thinning of roofs in caves at the upper level (Zhang Mingquan 1993).
Engineering Geology. Surveys were carried out to study the structure and stratigraphy of the Mogao grottoes and damage to them. Studies of the physical and mechanical properties of the cliff rock were also conducted (Zhou 1993). Tectonic and seismic analyses, and earthquake predictions in recent years, indicate that there could be an earthquake of 6.5 to 7 on the Richter scale in the Hexi Corridor area in the future. For this reason, mechanical-type concrete strain gauges were installed at observation points along major crevices in the Mogao bedrock to monitor stability. A seismic recorder was set up to record seismic activity, analyze vibration resistance of the cliff rock and reinforcement structures, and evaluate earthquake hazards in the region (Yao 1993).
Wind monitoring. Wind direction and speed, windblown sand on the plateau, and the quantity of sand transported were continuously monitored using the weather station data and monitoring devices.
Material analysis of the paintings and polychrome sculpture.
Analysis was performed on the support layer, the ground layer, and the pigment layer of the wall paintings and the polychrome statues. The types, structures, and characteristics of the binding media mixed in the pigments were also scientifically analyzed (Guo 1993b; Xu 1993; Li Shi 1993).
World History
