Karst refers to the processes of chemical dissolution and mechanical erosion acting on soluble rocks (mainly carbonates and evaporites), and to the surface and subsurface landforms thus produced. In their book Karst Hydrogeology and Geomorphology, Derek Ford and Paul Williams state that about 20 percent of the emerged Earth’s surface is karst, with caves representing a typical and well-known expression (see Ford and Williams 2007, cited under Karst Hydrogeology: The Importance of Karst Aquifers). Together with caves, karst lands are characterized by underground drainages and by scarce presence of water running at the surface. Water, rather than flowing on the ground as watercourses and rivers, rapidly infiltrates underground through networks of fissures and conduits, which combine to the diffuse flow in recent carbonates, giving origin to the complex systems of karst caves. Karst environments and caves have been of interest to humans since the earliest civilizations—for water supply, as settlements or areas of protection, or to bury the dead. Some of the more ancient testimonies of art are within caves, such as those in several caverns of the Mediterranean area (including, to mention the most remarkable, Lascaux and Chauvet in France, Altamira in Spain, and Porto Badisco in Italy). Karst research, which is linked to caving exploration, had a great impulse in the second half of the 20th century. Caves have been recognized as a very precious and peculiar environment, where traces of the past, in terms of sediments (see Sasowsky and Mylroie 2004, cited under Cave Deposits) or evidence of paleoclimate (see Fairchild and Baker 2012, cited under Contribution to Paleoclimatic Studies), have been preserved, often in great detail, in contrast to what occurs at Earth’s surface, where most of it is being destroyed, canceled, or covered by later processes. As a consequence, the classical studies about speleogenesis (that is, the origin of caves) and on geomorphology of the underground settings have developed in integration with those by researches in other disciplines, covering, among others, cave sediments, biospeleology and microbiology, and dating of speleothems for paleoclimatic and paleoenvironmental studies. Further, the expansion of built-up environments and construction in karst lands resulted in the interaction among natural hazards in karst and society, as pointed out in Parise and Gunn 2007 (under Karst Hazards), and Gutiérrez, et al. 2014 (under Human Impacts and Land Management in Karst), bringing to general attention the issue of fragility of karst, due to its peculiar hydrologic and hydrogeological features. As a matter of fact, Goldscheider and Drew 2007 (under Karst Hydrogeology: The Importance of Karst Aquifers) documents that karst aquifers are of high quality and represent between 20 and 25 percent of the world’s drinking resources, but that they are also extremely vulnerable and potentially threatened by a variety of forms of pollution.
Hydrochemical evaluation of water resources and human impacts on an urban karst system, Jordan