Types And Origin Of Cavities On Cliffs In The Danxiashan UNESCO Geopark

The Mt.Danxiashan is a UNESCO Global Geopark and representative of the World Heritage ‘China Danxia’,which is also considered to be the demonstration area for international Danxia landscape studies.Previous research has been mostly focused on the geologic evolution,scenery landscape distribution and morphologic description,and biodiversity,which enhanced tourism development in recent years.Cavities of various sizes and morphologies along the red beds cliffs have attracted great interests of scientific community and tourists alike.The cavities include bedding-controlled cavities,arches,vertical cavities,and tafoni,etc.A lot of them were qualitatively described in previous publications,but a few studies used quantitative experiments.As a result,their formation processes remain ambiguous.In this work,cavities along the cliffs of the Danxiashan Global Geopark were investigated by field survey,size measurement of cavities,meteorologic monitoring,in-situ rock rebound measurement,and laboratory experiments including microscopic observation,conductivity,ion concentration of water-soluble salts so as to interpret formation processes.The cavities are grouped into six genetic types,namely fracture-,fracture and bedding-,bedding-,water erosion-and,weathering-corrosion-,and colluvial stacking-types.The formation and evolution of Danxia landscapes are dominated by tectonic activities.Meanwhile,lithology is considered fundamental.Water flows not only have erosive effects on slopes,but also enhance hydrolysis and chemical dissolution in tandem with water seepage within rock,eventually resulting in sandstone weathering and decay.The colluvial stacking-type cavities are different from others in formation.Generally the inner of tafoni is featured by less ranges of temperature and relative humidity,higher water-soluble salts and lower rebound values than the outer.As a result,the moist inner of tafoni have been weathered faster than the dry outer,thus they apparently tend to grow inward and upward.The quantitative experiments of cavities along cliffs of this work provide solid evidence for interpretation of their formation processes.The results can be used to update scientific popularization content of the Mt.Danxiashan and similar landscape scenic areas,which would be favorable for popularization education of geosciences,and meet the demand of tourist interest in travel.