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Role of mixing corrosion in calcite‐aggressive H 2 O‐CO 2 ‐CaCO 3 solutions in the early evolution of Karst Aquifers in limestone
Author(s) -
Gabrovšek Franci,
Dreybrodt Wolfgang
Publication year - 2000
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/1999wr900337
Subject(s) - calcite , karst , dissolution , mixing (physics) , cave , corrosion , geology , aquifer , mineralogy , kinetics , materials science , chemistry , groundwater , geotechnical engineering , metallurgy , physics , paleontology , archaeology , quantum mechanics , history
Two cave‐forming mechanisms in limestone are discussed currently. First, when two H 2 O‐CO 2 ‐CaCO 3 solutions, saturated with respect to calcite but with different chemical compositions mix, renewed aggressiveness to limestone dissolution occurs. This process called mixing corrosion [ Bögli , 1964, 1980], in combination with linear dissolution kinetics, has been suggested as cave forming. Second, it has been shown that solely the action of nonlinear dissolution kinetics can generate extended karst conduits. This paper combines both mechanisms. By digital modeling of the evolution of the aperture widths of a confluence of two fractures into a third one it is shown that the first mechanism does not create large cave conduits. The combination of mixing corrosion and nonlinear kinetics, however, considerably intensifies karstification, compared to that of nonlinear kinetics solely. The times to terminate early evolution of karst are significantly reduced when the CO 2 concentrations of the inflowing solutions differ by no more than 30%. We discuss the underlying mechanisms by inspection of the time dependence of the evolution of aperture widths, flow rates through them, and of the renewed undersaturation of the mixed solution at the confluence of two fractures. Finally, the evolution of a karst aquifer on a two‐dimensional percolation network is modeled when mixing corrosion is present, and compared to that on an identical net with identical nonlinear dissolution kinetics, but mixing corrosion excluded. Large differences in the morphology of the net of cave conduits are found and also a reduction of the time of their evolution. From these findings we conclude that climatic changes, which influence the p CO 2 in the soil, can divert the evolving cave patterns.