Genesis Of Tafoni On Steep Slopes Of Danxia Landscapes In Humid Areas

Tafoni are a type of cavernous weathering features widely distributed in different climate environments around the world.Tafoni often form eye-catching landscapes,and they are also carriers of many historical cultures.At the same time,it is also one of the hot issues in the study of rock weathering in geomorphology.However,owing to differences in research methods and degrees,the origin of tafoni is still controversial.In this paper,large tafone on the red thick conglomerate cliffs in the Danxiashan and Cuiwei Peak,located within the subtropic humid region of South China,were selected for this research.Meteorological observation,field investigation,in-situ rebound test,humidity measurement and were carried out in the field,and microscopic observation of rock samples and salt chemistry test were carried out indoors.the role of rock structure and composition,micro-environment and weathering in the process of tafone weathering is discussed,and the formation process and stages of tafoni are discussed.Meteorological data show that compared with the external intense environmental changes,the interior of the tafone is in a micro-environment with small temperature and relative humidity ranges,high humidity and windless condition,which is conducive to the accumulation of water and salt,and is suitable for the further development of the tafoni.Tafoni have well ellipsoidal,elliptical and subrounded openings.Clasts of the conglomerates are low roundness,poorly sorted,and the cement is mainly composed of calcite and iron oxide.The degree of weathering of tafoni is high,and the hardness of the lip and column is similar,which is slightly higher than that of the backwall.The humid climate brings abundant moisture and salt to the tafone of Mt.Danxiashan and Cuiwei Peak.The measurement results of electrical conductivity and soluble salt test show that the main salts involve plaster（Ca SO₄）,mirabilite（Na₂SO₄）and rock salt（Na Cl）,which migrate in conglomerate pores and fissures and undergo reactions such as hydration and dissolution in moist conditions.The frequent salt crystallization within conglomerates broke the integrity of the rock and enhance further weathering.The conglomerates are highly porous and permeable,which are the rock foundation for the development of tafoni.The climatic environment and tafoni morphology are conducive to promoting water utilization efficiency and enhancing salt weathering.Case hardening is present in the cavernous weathering,but it might not be a key factor.The rock internal moisture plays an important role in tafoni morphology and is responsible for the upward and inward growth of tafoni.Therefore,the tafoni were not controlled by a single weathering factor but they should be the result of interaction between multiple agents.