The development of karst is a complex system driven by the dissolution of a host rock and the subsequent removal of dissolved matter by moving water. It is the process that, at various stages, initiates or triggers associated processes including erosion, collapse and subsidence. The dissolution of sulphate rocks proceeds by different mechanisms and at different rates to those associated with the dissolution of carbonate rocks. For each rock type different factors influence the process. This chapter is an attempt to summarise the present knowledge of the dissolution chemistry and kinetics of gypsum and anhydrite. These are important for the genetic interpretation of karst features in these rocks. The gypsum-anhydrite-gypsum transitions and recrystallization processes are also addressed, because of their importance to karst development.

Definition of karst in gypsum and explanation of different types of karst in gypsum: intrastratal, exposed, covered, buried, exumed and palaeokarst.

Detailed explanation of hydrogeological characteristics of gypsum aquifers is given in various situations: deep-seated karst-confined conditions, subjacent, entrenched and denuded karst types-semi-confined, phreatic and vadose conditions. The hydrogeological evolution of barren exposed gypsum karst and flow velocities in gypsum karst aquifers is also discussed.

Medium- to large-size forms in gypsum karst are described, including dolines, blind valleys, ploje-like depressions, collapses and positive and/or residual forms such as outliers, cone-like hills, dome-like hills, mesa-like tabular blocks and plateaux and breccia pipe hills. The similarities and/or difference between gypsum and carbonate forms are discussed.

Intrastratal karst is by far the predominant gypsum karst type. Its development may begin in deep-seated settings within rocks already buried by younger strata, and it proceeds increasingly rapidly as uplift brings gypsum sequences into progressively shallower positions. Such development commonly occurs under confined (artesian) hydrogeological conditions, that subsequently change to open conditions (phreatic-water table-vadose). The general evolutionary line of intrastratal karst is typified by progressive emergence of a sequence into a shallower position, activation of groundwater circulation and development of cave systems within karst units, commencement of gravitational breakdown and its upward propagation through overlying beds, and development of a karst landscape. These processes and phenomena progress through the directed evolution of karst types as follows: deep-seated intrastratal karst (1K) to subjacent 1K to entrenched 1K to denuded karst. One of the main characteristics of intrastratal karst is that it induces gravitational breakdown in cover beds. With the aid of processes other then simple breakdown, such effects may propagate upwards and may, or may not, reach the surface, depending upon the thickness and structure of the overburden. A karst landscape evolves when such features reach the surface. This paper considers the conditions and mechanisms of such development.

Short description of caves and karsts in gypsum of different parts of the World.

In Great Britain the most spectacular gypsum karst development is in the Zechstein gypsum (late Permian) mainly in north-eastern England. The Midlands of England also has some karst developed in the Triassic gypsum in the vicinity of Nottingham. Along the north-east coast, south of Sunderland, well-developed palaeokarst, with magnificent breccia pipes, was produced by dissolution of Permian gypsum. In north-west England a small gypsum cave system of phreatic origin has been surveyed and recorded. A large actively evolving phreatic gypsum cave system has been postulated beneath the Ripon area on the basis of studies of subsidence and boreholes. The rate of gypsum dissolution here, and the associated collapse lead to difficult civil engineering and construction conditions, which can also be aggravated by water abstraction.

Description of gypsum karst and caves in Germany

Gypsum karst has been studied in Italy since the last decades of the l9th Century. In 1917 the geographer Olinto Marinelli published �Fenomeni carsici delle regioni gessose d�Italia�, a fundamental synthesis of the early research. He distinguished 56 different morpho-karstic gypsum units and/or areas, which are all different in size and character, and described them, paying special attention to their surface morphology and hydrology. Marinelli listed all the main gypsum units and only a few secondary outcrops were overlooked. After Marinelli�s synthesis, except for some discussion of archaeological caves, only a few papers about gypsum karst and environment were published until the nineteen-fifties. In the nineteen-sixties and seventies much exploratory work and documentation was carried out in the Emilia Romagna area, principally devoted to the gypsum caves, and undertaken by the local speleological clubs and university researchers. The chapters that describe gypsum karst surface landforms in this publication contain many references to examples of gypsum karst in Italy, and these supplement the descriptions provided below.

The great gypsum karst of the Western Ukraine, which is associated with Miocene (Badenian) gypsum, provides the worlds foremost examples of intrastratal gypsum karst and speleogenesis under artesian conditions. Differential neotectonic movements have resulted in various parts of the territory displaying different types (stages) of intrastratal karst, from deep-seated, through subjacent, to entrenched. Internal gypsum karstification proceeded mainly under confined hydrogeological conditions. While such development still continues in part of the territory, other parts exhibit entrenched karst settings. Huge relict maze cave systems have been explored here, five of which are currently the longest known gypsum caves in the world. They account for well over half of the total length of gypsum cave that has been explored. This unique concentration of large caves reflects the local coincidence of specific structural prerequisites of speleogenesis (character and extent of fissuring), favourable regional evolution (rapid uplift, and fossilization of maze systems), the presence of overlying limestone aquifers, and a widespread clayey protective cover (which prevented the total infilling and/or destruction of the caves). Surface karst evolved as a consequence of the internal karstification in the gypsum, and the karst landform assemblages differ between the territories that present different types of karst.

Description of the gypsum karst of the pre-Ural region in Russia, with special emphasis on speleogenesis.

The Peoples Republic of China has the largest gypsum resources in the world and a long history of their exploitation. The gypsum deposits range in age from Pre-Cambrian to Quaternary and their genesis includes marine, lacustrine, thermal (volcanic and metasomatic), metamorphic and secondary deposits. The gypsum is commonly associated with other soluble rocks such as carbonates and salt. These geological conditions, regional climate differences and tectonic setting strongly influence the karstification process resulting in several karst types in China. Well developed gypsum palaeokarst and some modem gypsum karst is present in the Fengfeng Formation (Ordovician) gypsum of the Shanxi and Hebei Provinces. Collapse columns filled with breccia emanate upwards from this karst and affect the overlying coalfields causing difficult and hazardous mining conditions. Gypsum karst is also recorded in the middle Cambrian strata of Guizhou Province and the Triassic strata of Guizhou and Sichuan Provinces. Gypsum-salt lake karst has developed in the Pleistocene to Recent enclosed basin deposits within the Qinghai-Xizang (Tibet) Plateau.