Karst is widely distributed in Vietnam,covering almost 60,000 km2,approximately 20％of the total area of Vietnam.Most karst rocks crop out in North and Central Vietnam.Karst developed with peak-clusters,peak-forests,caves,etc.is sparsely distributed in the south of Vietnam.Based on previous research,the geological map of karst distribution in Vietnam was drawn up,combined with remote sensing image,geological map,and cave atlas.In terms of geological structure,lithology combination,hydroclimate in Vietnam,conditions of karstification in this country were analyzed.From the perspective of regional geology,the characteristics of karst geology and geomorphology,karst distribution and the present situation of karst resources in Vietnam were investigated.Karst in Vietnam is distributed in the tropical karst belt,with similar origins of karst in South China.The distribution law of karst in Vietnam is mainly controlled by stratigraphic lithology and tectonic movement.Karst is developed in all the pre-Cambrian and Holocene strata and the pure limestone strata of Carboniferous,Permian and Triassic with a thickness of 1,000-2,000 m are the main beds of karst development.The warm and rainy climate and rich biological diversity accelerate karstification.There are four major karst zones in Vietnam,including peak-clusters and peak-forests in the northeast,peak-forests in Ha Long Bay and karst mountain along Truong Son Ra karst in the northwest.The karst area in northeast is an extension of the karst from South China,with the development of alpine karst landforms,peak-forests,peak-clusters,large drainage gullies and sinkholes.Sinkholes are extremely developed,with an average 1.4 sinkholes per square kilometer.The karst landforms vary from plateaus to depressions and hills and finally to plains from northwest to southeast,showing a complete evolution of tropical karst geomorphology.There are karst landforms such as large and deep poljes,deep gullies and caves.The vertical distance of Conh Nuoc cave,the deepest cave,is 600 m.The peak-forest along Ha Long Bay is an extension of the peak-forest of South China.In the central part,karst is distributed along the Truong Son Ra.Phong Nha Cave currently known as the longest cave in Vietnam is located in the famous karst area of Phong Nha-Ke Bang.The Phong Nha cave system is composed of 20 caves,more than 60 km in length,where is located the longest river cave and the cave with the largest passage in the world.Vietnam is rich in karst water,karst mineral and karst landscape resources.At present,karst water has become the main water source for industry,agriculture and life in Vietnam,but water supply is in serious shortage,especially in the dry season.Vietnam is at an advanced level in the exploitation of karst mineral resources and is currently the eighth largest cement producer in the world.Remarkable achievements have been made in balancing regional economic development and ecological protection,and a series of world geological heritage reserves and national ecological reserves have been established in karst areas.
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