Description:

Karst systems in carbonate rocks are formed in the presence of water that is charged with carbonic acid. In karst hydrology it is well known that the main sources of this CO₂ are the activity of microorganisms in the soil and root respiration of plants. Karst hydrologists are challenged to explain why large cavities form deep inside the cave, even if the water has a limited dissolving capacity. There are currently two accepted explanations. The first is called "mixed corrosion" and is explained by the calcite-aggressive behavior of waters that mix from two streams of water, each in a calcareous-carbon equilibrium.

This can happen, for example, in joints. The mixed water then has new potential to dissolve further carbonates and form cavities. A second explanation assumes nonlinear dissolution kinetics, stating that water would retain some of its potential to dissolve carbonates while penetrating deep into the rock. A new approach for transporting CO₂ to deeper layers of the earth without percolating meteoric water was recently proposed by us (Class et al., 2021) and is concerned with the dissolution of CO₂ at the epiphreatic karst water table and the independent CO₂ mobility and its density-driven sinking in the water column (NERO from nerochytis/sink - Greek).

This karst water, which is loaded with additional CO₂, leads to the formation of new cavities with their typical round, phreatic wall and ceiling shapes. This morphology can be seen impressively in many fossil caves, e.g. in the Swabian Jura, Germany's largest karst area. Our preliminary work in the system CO₂-water has confirmed the plausibility of the new hypothesis. In order to underpin the relevance compared to "classic" theories, the system CO₂-water-carbonate is examined in the laboratory, in the model and in the field as part of the project.

Class, H., Bürkle, P., Sauerborn, T., Trötschler, O., Strauch, B., Zimmer, M. (2021) On the role of density-driven dissolution of CO₂ in phreatic karst systems. Water Resources Research, DOI: 10.1029/2021WR030912

Duration of project: 01/2023 – 12/2025

Funding: DFG 508470891

Cooperation partners:

apl. Prof. Dr.-Ing. Holger Class University of Stuttgart, Institute for Modelling Hydraulic and Environmental Systems

Harald Scherzer Höhlen- und Heimatverein Laichingen e.V.  (in German only)