『Abstract
　The dominant factors affecting the development of weathering forms on the Pravcice（最初のcの頭にv） Rock Arch (PRA) (Bohemian Switzerland National Park, Czech Republic) are discussed, based on the in situ monitoring of weathering forms, as well as on laboratory studies of materials taken from this site. The in situ monitoring shows the progressive development of distinct weathering forms (delamination of case-hardened rock surfaces, cyclic efflorescence, and granular disintegration of exposed weakly cemented rock mass) in specific portions of the PRA, whose location is controlled by lithology, jointing/local hydrodynamics, and exposure to climatic factors. From the analysis of efflorescence, the dominance of sulphates is evident; particularly of gypsum and alums. However, the synergistic effects of the several salt species (that also include minor nitrates and chlorides) upon the mechanical disintegration of sandstone can be expected.

Keywords: Upper Cretaceous sandstone; Rock arch; Bohemian Cretaceous basin; Weathering processes; mineralogy of efflorescence; Water soluble salts chemistry』

Introduction
Study area
　Geology, lithology and morphology
　Climatic conditions
Weathering forms of the Pravcice（最初のcの頭にv） Rock Arch
　Case-hardened rock surface
　Blistering, delamination and salt crystallization
　Colour changes of the rock surface
Methodology
　Monitoring of weathering processes
　Sampling
　Laboratory study of case-hardened rock surface and salt efflorescence
　　X-ray diffraction
　　Determination of water-soluble salts
　　SEM/EDS study
Results of the laboratory study
　Phase and chemical composition of efflorescences
　Chemical composition of subflorescences
　SEM study of weathering forms
Discussion
　Factors influencing development of the PRA relief
　Monitoring and maintenance of the PRA
Conclusion
Acknowledgments
References