This study gives a general description of karst types. Thus, the hierarchical classification and structure of karst types, the characteristics of their stability, their development and transformation, and the relationship between the climate and karst types are overviewed.

The significance of geodiversity [1,2,3,4], to which karst also contributes, is given by the fact that it is the basis of the survival of biodiversity [5]. Karstifying rocks are widespread on the Earth (Figure 1). Karst areas can be put into karst types. The analysis of karst types enables better knowledge of karst diversity. However, the general description of karst types may also be an effective tool for a global overview of the karstic and the non-karstic processes working in karst areas. The concept of a karst type is based on a characteristic feature of karsts that some characteristics of certain karst areas and thus their karstification show similarities, while they can be significantly separated from other karst areas regarding other characteristics.

During research, various karst types were distinguished and described [7,8,9,10,11,12,13,14,15,16]; their comprehensive classification was made by Veress [17]. When karst areas are classified as karst types, the following are considered: altitude of karst, its geological characteristics (rock, structure), climate, hydrology, morphology, and geomorphic evolution. In some cases, various type names do not refer to other karsts (karstic content), but the different characteristic features of the karst area resulted in manifold terminology. Classification into types is based on some characteristics of the karst area, while putting the same karst area into another type is made according to other characteristics. Thus, the type names of geosynclinal karst and high mountain karst (mountain glaciokarst as well) refer to the same karst areas. The denudation of karst rocks happens by the process during which the rock gets into solution. At geosynclinal type, karst structure, at high-mountain type, climate-vegetation zonality and soil zonality, while at glaciokarst, the existence of glacial surface development are the viewpoints that determine classification. The dissolved material precipitates, while being transported to different distances. The dissolution intensity depends on rock characteristics (rock structure like fractures and faults are the most important discharge sites of the karst, but dissolution also takes place along them). However, it also depends on rock quality (evaporates are dissolved more intensively than carbonate rocks) and on the CO₂ content of water on carbonate rocks [12]. Since the CO₂ content decreases farther from the Equator through the intensity of soil life, the diversity, size, and density of karst features decreases farther from the Equator (and from the sea level) [18].

On karst, a spatially developed hydrology develops, but its surface is poor in streams because of the infiltration of meteoric water. The infiltrated water fills the gaps and cavities, created by itself, and its surface is the karstwater level. Its elevation is determined by the altitude of the surrounding terrain and it constitutes the base level of erosion of the karst together with it.

Karst areas are characterized by cavity formation, but the landscape is specific: surface features are mostly arheic. (It should be noted that if the karst is covered, features different from uncovered karst also develop in its area.) Arheic features are for example ponors, dolines, and poljes, while open features are karren and intermountain plains [14]. However, among karst features can be mentioned remnant features such as inselbergs or the remnants of cave ceilings, the arches [19].

All areas built up of soluble rocks can be regarded as karst. These rocks are limestone, dolomite, gypsum, anhydrite, halite, calcareous conglomerates, and marl. These are dissolved by carbonated water and other acids (for example sulfuric acid, which is released during dissolution of rock with pyrite content) or only by distilled water. However, alkaline water can also have a dissolution effect on sandstones and conglomerates.

Because of their water storage capacity, karst areas have a significant role in drinking water supply, especially in areas with a dry climate. Paleokarst features have economic significance. They are sediment raps of minerals like bauxite, manganese, etc. [20,21].

Caves develop during underground, mainly dissolution, processes. These caves are significantly different in size, particularly on limestone karsts. They are also genetically diverse thus there are of ponor caves, spring caves, through caves, foot caves, etc. [12,19,22]. They often have an important role in the development of karst types (hypogene karst). In other cases, caves participate in karst type formation together with surface karst.

In addition to dissolution, non-karstic effects also take place on the karst for a shorter and a longer time. The type of effects is climate dependent. Thus, on temperate and cold-climate karsts, frost weathering, mass movements, and fluvial erosion are also widespread. The latter occurs if the karst is covered or the karstwater level is at the valley floor. In areas above the snow limit (the altitude of which depends on the distance from the Equator and on the Earth’s global climate) glacial erosion is the main geomorphic agent. After ice regression too, glaciokarsts develop.