ABSTRACT:

This is a study to conserve the Dunhunag Mogao Grottoes in the arid region of China. The wall paintings in the caves are severely deteriorated by recrystallization of salt that is accumulated by the evaporation of moisture in the rock formation. Our aim is to understand the moisture movement from the Qilian Mountains to the Mogao Grottoes through the observation of the fault system and vegetations by satellite remote sensing. In this study, Landsat5-TM and Terra-Aster data are used for analyzing geological structures and vegetations in wide area. The NDVI map, which is analyzed by Quick Bird data, is useful to understand distributions of natural vegetation. In spite of low rainfall locally, significant natural vegetations grow up not only along the river but also on the sand dune and basement rock. We illustrate that some vegetations are distributed on the fault systems as straight lines in the Sanwei Mountains. These results indicate that moisture moves along the fault systems and the vegetations absorb it and grow on the faults. It is conceivable that moisture moves through the Mingsha Mountains, which have the same geological features as the Sanwei Mountains. And it indicates the possibility that moisture reach to the Mogao Grottoes from the southwest.

1. INTRODUCTION

The Mogao Grottoes is located on the southeastern margin of the Dunhuang oasis, 25km from Dunhuang city. Dunhuang is on the Silk Road, on the edges of the Taklamakan Desert, in Gansu province, China. Many of the stone monuments in arid areas are damaged by salinity. The Mogao Grottoes, which is famous for wall paintings and murals also, has the problem. The wall paintings in some caves are severely deteriorated through the recrystallization of salt. And plaster-flaked walls are found in several caves. This is caused by moisture movement into the rock which is a conglomerate of alluvium. Our monitoring shows that although the surfaces show the low humidity of 30% to 35%, the humidity at the depth of 30 centimeters in the drill holes is almost 95% to 100% [1]. This result indicates that the moisture content is supplied from inside of the rock formation. There are four sources from which water and moisture come to the Mogao Grottoes: water from the Daquan River, rain water from the top of the cliff, moisture moving through the pores in the permeable rock formation and through the fissures, and irrigation water for the vegetation in front of the caves. Tanimoto, et al maintain that the water and moisture are supplied through rock joints and fissures which were formed by fault activity by using satellite remote sensing and field survey[1]. When water systems are surveyed in an arid area, it is difficult to confirm the flow of the surface water except for the mainstream. Therefore it is important to recognize the existence of small springs and natural vegetations on the surface and estimate moisture movement in the ground. The purpose of this study is to interpret the relationship between fault systems and natural vegetations by using satellite remote sensing and field survey, and understand the ways of the water and moisture movement in the permeable rock formation and fissures in this arid region.

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