Speleogenesis and Hazards in Karst: Observing, Modeling, Predicting

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Carbonate and sulfate bedrocks cover more than 10% of the land surface of the Earth. The bedrocks, which provide water for 25% of the world’s population, can be dissolved by water. The dissolution process, termed karstification, largely controls the evolution of the karst region. In a karst landscape, water disappears from the surface, and on its way down it is enriched by carbon dioxide from the atmosphere and the soil. The resulting weak carbonic acid is able to dissolve carbonate rocks, both on the rock surface and within small fractures in the rock. The enlargement of fissures and bedding planes through chemical dissolution of calcite results in a dramatic increase in permeability of the rock, and with time more and more water is captured and carried subsurficially through enlarged fissures and bedding partings. The evolution of a karst system occurs in distinct steps: (i) Initially, water mainly runs off the surface towards a regional base level, e.g. a river. Flow through the aquifer is diffuse and slow. The evolution of the karst surface is effective due to the surface runoff. (ii) With time, the chemical dissolution has enlarged subsurface structures (fissures, bedding planes), and the secondary porosity increases manyfold, with subsurface flow becoming dominant. Enlarged fractures become cave systems, which efficiently drain the catchment, and water is rapidly carried to large karst springs. Surface runoff becomes episodic and will be sparse. In this project, karstification is simulated with a numerical model, the KARST 1 tool, which describes flow and evolution on and in the karst system. The numerical algorithm will simulate typical characteristics of a karst landscape, such as landscape evolution including erosion, diffusion, and denudation, as well as flow and transport in the enlarged fissures and bedding planes and the rock matrix. An attempt will be made to generate specific karst settings such as shallow and deep karst aquifers of the Swabian Alb in South Germany, but also deep alpine systems such as the long cave systems in the Swiss Alps.