Principal Characteristics of Hypogenic Speleogenesis

Two principal types of karst systems, hypogenic and epigenic, are regularly associated with different types, patterns and segments of flow systems, which are characterized by distinct hydrokinetic, chemical and thermal conditions. Epigenic karst systems are predominantly local systems. Hypogenic karst is associated with discharge regimes of regional or intermediate flow systems dominated by upward flow, although mixing with local systems is commonly involved. Hypogenic speleogenesis tends to operate over long time spans, continuously or intermittently. Its main characteristic is the lack of genetic relationship with groundwater recharge from the overlying or immediately adjacent surface. Hypogenic karst may not be expressed to the surface and is largely climate-independent.

Hypogenic speleogenesis is the formation of solution-enlarged permeability structures by waters ascending through soluble formations from below. Vertical hydraulic communication across lithological boundaries and different porosity systems allows deeper groundwaters in regional or intermediate flow systems to interact with shallower and more local systems supporting various dissolution mechanisms. There is a specific hydrogeologic mechanism inherent in hypogenic transverse speleogenesis (restricted input/output) that suppresses the positive flow-dissolution feedback and speleogenetic competition in initial flowpath networks, accounting for more uniform and pervasive conduit development.

Hypogenic caves are identified in various geological and tectonic settings, being formed by different dissolutional mechanisms operating in various lithologies. Despite these variations, resultant caves demonstrate remarkable similarity in patterns and meso-morphology, strongly suggesting that the type of flow system is the primary control. Cave patterns in hypogenic speleogenesis are guided by the initial permeability structure and its vertical heterogeneities. Because of its "transversal" nature hypogenic speleogenesis has a clustered distribution in a plan view although clusters may merge and extend through large areas.

Recognition of wide occurrence, importance and specific characteristics of hypogenic speleogenesis represents a major paradigm shift in karst science that answers many questions not satisfactorily addressed previously.