Présentations Colloques

Oral Presentation
8.05
Session 8.05: Karst aquifers
Sharp John M.
Volcanogenic Karst Systems
Hypogenic karst forms from water flowing upward from depth. Several geologic conditions facilitate hypogenic karstification by sourcing acids that dissolve carbonate rocks at depth. Hydrothermal, deep-seated karst is now documented, but the processes are not commonly applied in geologic evaluations. Shallow magmatic and volcanic activities provide conditions that can dissolve large voids deep below the Earth's surface. Volcanogenic karstification has produced some of the Earth's deepest underwater cave systems. Volcanogenic karst systems (VKS) in Mexico (Sistema Zacatón), Australia (Mt. Gambier), Turkey (the Obruks), Italy (Pozzo del Merro), the Czech Republic (Hranice Abyss) and Russia (Blue Lake) have commonalities. Volcanogenic karstification needs four components to initiate and develop deep, subsurface voids- 1) thick carbonate strata+ 2) preferential groundwater flow paths (fractures fault zones)+ 3) volcanic igneous activity that releases acids, and 4) flux of groundwater through the system. Components 1, 2, and 4 are common to most karst, but component 3 can accelerate dissolution processes. The high fluxes of carbonic, sulfuric, and other acids can create hyper-aggressive subsurface conditions that can rapidly dissolve carbonates. The Hranice Abyss differs in that the CO2 is from a deep source not associated with shallow volcanic activity. **Compared to adjacent epigenetic karst, VKS can be somewhat isolated from surrounding epigenetic karst both physically and chemically+ have different speleothems and water chemistries+ and, when actively forming, the waters have higher temperatures and uniform characteristics with depth. Differences in the durations and magnitude of volcanic emissions, whether or not the processes are currently active, and geologic controls (i.e., fracture systems, etc.) create variations. With time, epigenic processes can overprint the VKS. Volcanogenic karstification can produce deep solution porosity and high permeability where older carbonate rocks are juxtaposed to younger volcanic rocks+ we infer that there remain undiscovered VKS at depths. **
United States