Volcanogenic Karstification: Implications of This Hypogene Process

Hypogenic karst forms from water in which the aggressiveness has been produced at depth, independent of acid sources at or near the surface. Numerous geologic conditions facilitate a setting for hypogenic karst processes to evolve, including the interaction of igneous rocks and groundwater in carbonate rocks. Hydrothermal, deep-seated karst is documented, but the mechanisms are not always applied in geologic evaluations. Volcanic activity provides conditions that can rapidly dissolve large voids deep below the Earth's surface. Volcanogenic karstification relies on four components to initiate and develop deep, subsurface voids: 1) thick carbonate strata, 2) preferential groundwater flowpaths (fractures), 3) volcanic activity that releases acids, and 4) flux of groundwater through the system. The order of occurrence (from 1 to 4) is critical to develop the karst. Components 1, 2, and 4 are common to almost all karst, but component 3 can accelerate dissolution processes. High fluxes of carbon dioxide and/or hydrogen sulfide from volcanic rocks create hyper-aggressive subsurface conditions that rapidly dissolve carbonate rocks. Volcanogenic karstification has produced the Earth's two deepest underwater cave systems, Pozzo del Merro (Italy) and Sistema Zacatón (Mexico). Studies of these processes require evaluation of systems currently active on or near the surface (directly accessible by humans or robots). Volcanogenic karstification can produce deep solutional porosity and high permeability where older carbonate rocks are juxtaposed to younger volcanic rocks.