Karst

Karst refers to a distinctive form of landscape produced by the dissolution of soluble rocks, most commonly limestone and dolomite. It is associated with a suite of characteristic surface and subsurface landforms, including closed depressions, disappearing streams, underground drainage systems and extensive cave networks. Such landscapes occur on every continent and are particularly noted for their dramatic scenery, complex hydrology and scientific significance in geomorphology, hydrogeology and petroleum geology. Karst terrains may also develop in more resistant rocks, such as quartzite, where particular environmental conditions permit prolonged chemical weathering.

Geological Basis and Processes of Formation

Karst develops primarily in dense carbonate rocks that contain fractures, joints and bedding planes along which groundwater can circulate. In regions with moderate to high rainfall, carbon dioxide in the atmosphere dissolves in rainwater to produce a weak carbonic acid solution. This solution absorbs additional carbon dioxide from soil respiration as it percolates through the ground, further increasing its acidity. The carbonic acid reacts with calcium carbonate in the bedrock, leading to a series of dissolution reactions that gradually enlarge pathways, forming conduits, shafts and subterranean channels.
Although dissolution by carbonic acid is the standard mechanism, other chemical processes may also play a role. In rare circumstances, oxidation of sulphides can generate sulphuric acid, which dissolves limestone more aggressively. This process is known in places such as the ancient Lechuguilla Cave in New Mexico and continues in the Frasassi cave system in Italy, where oxygenic waters interact with sulphide-rich environments. The reactions may ultimately form gypsum, produced by the transformation of calcium sulphate resulting from sulphuric acid corrosion.
Karst development is strongly influenced by hydrogeology. Areas with low water tables allow water to descend rapidly, preventing saturation and maintaining dissolution efficiency. Conversely, where groundwater becomes saturated with carbonate minerals, dissolution slows significantly. Environments with thin or permeable vegetation cover and entrenched river systems particularly favour karstification.

Major Surface and Subsurface Landforms

Karst landscapes display a wide diversity of geomorphological features, ranging from small-scale solutional forms to large dramatic structures. Fine-scale features include solution flutes and rillenkarren, which appear as linear grooves etched into exposed limestone, as well as clints and grikes forming classic limestone pavements. Kamenitzas, shallow dish-like depressions, are also common on bare rock surfaces.
Medium-scale landforms include closed basins, vertical shafts, sinkholes, dolines and cenotes. Such depressions often mark points at which surface water flows underground. Disappearing streams and re-emerging springs are characteristic components of karst hydrology, reflecting the dominance of subterranean drainage.
At a larger scale, karst regions may contain extensive poljes—flat-floored depressions that can stretch for several kilometres—alongside deep karst valleys and mogote or tower karst landscapes. Tower karst is especially striking in tropical regions such as southern China, Thailand and Vietnam, where isolated, steep-sided limestone towers rise dramatically above alluvial plains. Similar formations occur in the Caribbean, including Cuba, Jamaica and Puerto Rico.
Beneath the surface, dissolution along fractures produces large cave systems, underground rivers and complex aquifers. The deposition of minerals within caves forms speleothems such as stalactites, stalagmites and flowstone. Rates of precipitation vary with humidity, water chemistry and cave ventilation. In certain landscapes, tufa terraces form where spring-fed rivers release dissolved carbon dioxide and deposit layers of calcite over long periods.

Global Distribution and Examples

Karst terrains are widespread, with notable concentrations in the Dinaric Alps of the western Balkan Peninsula, where the term “karst” originated. This region, spanning parts of Italy, Slovenia, Croatia and several neighbouring countries, contains classic examples of poljes, dolines and underground river systems. Tower karst and fengcong landscapes are best known from the South China Karst, including the Guilin region, designated as a World Heritage Site for its outstanding geomorphology and biodiversity.
Other major karst areas include the causses of southern France, the gypsum karst of Spain, the castillan meseta, the limestone plateaux of South Wales and the cone karst landscapes of Southeast Asia. Coastal karst, including makatea formations, is particularly well developed in tropical island settings where bioerosion and wave action shape cliffs and undercut terraces.

Etymology and Early Scientific Study

The word “karst” entered English via German in the nineteenth century. It originally referred to the Karst Plateau, a limestone region located between Italy and Slovenia and forming part of the Dinaric Alps. Linguistic evidence suggests that the term derives from a Romanised Illyrian root associated with mountainous or stony landscapes. The Slovene form was recorded as early as the twelfth century, reflecting the long-standing recognition of the region’s distinct topography.
Early systematic study of karst phenomena began in central Europe. Johann Weikhard von Valvasor introduced the term to a wider scholarly audience in 1689 in his description of underground river flows associated with Lake Cerknica. In the late nineteenth and early twentieth centuries, Jovan Cvijić advanced karst geomorphology substantially. His 1893 work on the landforms of the Balkan karst provided detailed classifications of dolines, karren and poljes, while his later publications proposed an influential erosion cycle theory for karst landscape development. From the mid-twentieth century onward, karst hydrology developed as a separate field, incorporating the insights of cave explorers and applying quantitative methods to the study of underground flow networks.

Specialised Forms: Interstratal, Salt and Tropical Karst

Interstratal karst occurs where soluble rocks are overlain by insoluble strata, such as sandstone. Dissolution may proceed at depth while the surface shows little or no karst expression. When the cover collapses or is removed, extensive doline fields may be exposed. In South Wales, for example, significant interstratal karst landscapes have formed beneath Twrch Sandstone, producing irregular surfaces now recognised for their geological significance.
Salt karst, or halite karst, develops in regions where underground salt layers dissolve, leading to subsidence and potentially hazardous collapses. Such areas are often unstable due to the rapid solubility of halite.
Tropical karst includes kegelkarst, cockpit karst and mogote formations. These landscapes occur where high rainfall and warm temperatures accelerate dissolution. The forests that develop on karst terrain are frequently rich in specialised flora, particularly orchids, palms and mangroves, due to the high pH of the thin soils and the relative isolation from human disturbance.

Paleokarst and Geological Significance

Paleokarst refers to ancient karst systems preserved within the stratigraphic record. Such features provide valuable information for reconstructing past environments and understanding geological processes. They often occur where intervals of non-deposition allowed exposure and dissolution of limestone, followed by burial under younger sediments. Successive cycles of exposure and burial can produce complex karst surfaces preserved in the rock succession.
Paleokarst is of particular importance in petroleum geology. A significant proportion of global oil and gas reserves is hosted within carbonate rocks, and many reservoirs owe their porosity to ancient karst processes. The presence of buried conduits, cavities and dissolution-enhanced fractures can strongly influence hydrocarbon migration and storage.