Karst

In the early days of planning of the international Square Kilometre Array (SKA) during the 1990s, the Chinese delegation vied to host the SKA, proposing to build several large dishes in the natural limestone depressions (karsts) that dimple its southwestern provinces, and called the proposal Kilometer-square Area Radio Synthesis Telescope (KARST). Chinese astronomers even did preliminary work on the FAST radiotelescope as a prototype. The countries hosting the SKA Telescope became South Africa and Australia. KARST would have consisted of about 30 individual elements, each about 200 meters in diameter. A site survey of 288 suitable locations was performed in Pingtang County, Guizhou Province.

fengcong (cone karst) in Guilin as part of the South China Karst Karst ( ) is a topography formed from the dissolution of soluble carbonate rocks such as limestone and dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. There is some evidence that karst may occur in more weathering-resistant rocks such as quartzite given the right conditions. Subterranean drainage may limit surface water, with few if any rivers or lakes. In regions where the dissolved bedrock is covered (perhaps by debris) or confined by one or more superimposed non-soluble rock strata, distinctive karst features may occur only at subsurface levels and can be totally missing above ground. The study of paleokarst (buried karst in the stratigraphic column) is important in petroleum geology because as much as 50% of the world's hydrocarbon reserves are hosted in carbonate rock, and much of this is found in porous karst systems. ===Chemistry of dissolution=== The carbonic acid that causes karst features is formed as rain passes through Earth's atmosphere picking up carbon dioxide ( ), which readily dissolves in the water. Once the rain reaches the ground, it may pass through soil that provides additional produced by soil respiration. Some of the dissolved carbon dioxide reacts with the water to form a weak carbonic acid solution, which dissolves calcium carbonate. The primary reaction sequence in limestone dissolution is the following: in Estonia In very rare conditions, oxidation can play a role. Oxidation played a major role in the formation of ancient Lechuguilla Cave in the US state of New Mexico and is presently active in the Frasassi Caves of Italy. on Dent de Crolles, France The oxidation of sulfides leading to the formation of sulfuric acid can also be one of the corrosion factors in karst formation. As oxygen-rich surface waters seep into deep anoxic karst systems, they bring oxygen, which reacts with sulfide present in the system (pyrite or hydrogen sulfide) to form sulfuric acid ( ). Sulfuric acid then reacts with calcium carbonate, causing increased erosion within the limestone formation. This chain of reactions is: (sulfide oxidation) (sulfuric acid dissociation) (calcium carbonate dissolution) (formation of calcium sulfate) (formation of gypsum) This reaction chain forms gypsum. ==Karst studies== The study of the various aspects of karst regions is called karst studies, karst science, or karstology. This includes biological, chemical, ecological, geomorphological, hydrogeological, hydrological, political, socio-economical, and other processes over a variety of spatial and temporal scales in karst regions, with the purpose of understanding karst aquifers and ecosystems, and the development of the surface and underground structure, so that the environment can be protected and human activities planned effectively. Prominent karst researchers include Jovan Cvijić and William Morris Davis.

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