Konwersatorium im. Leopolda Infelda

Limestone rock is dissected by many narrow fractures, both horizontal and vertical, with aperture widths in the order of 0.1 mm. Water loaded with carbon dioxide penetrates into these fractures as a weak acid and can widen them by chemical dissolution of CaCO3. This process creates spectacular karst landscapes hosting caves and underground rivers. A model based on the hydrodynamics of flow in fracture systems and its coupling to dissolution of limestone is presented. From this model one can understand the processes by which caves and limestone aquifers originate. The model can be applied to a variety of geological and geochemical scenarios.

First, a short introduction into the chemistry of dissolution kinetics of calcite (CaCO3) in water containing carbon dioxide is given. As basic element of the model widening of a single plane parallel fracture is derived. Then the evolution of cave systems originating from local water inputs on a limestone plateau is presented. As a second building block of karst evolution it will be shown how an aquifer develops from evenly distributed input of rain water to the surface of a limestone plateau. In a third scenario the concept of mixing corrosion is applied to explain the origin of isolated caves without entrance and exit in Florida.Finally we use the model to discuss the risk to the operation of dam sites by evolution of karst conduits below the dam due to the high pressure by the impounded water. This can cause unbearable loss of water and endanger the structure of the dam.