Abstract:

This paper reviews the hydrochemical processes that determine the patterns of caves and other solutional features within carbonate rocks. The model presented relies on the functional relationships expressed by chemical mass balances, flow equations, and kinetic expressions for dissolution rate. Although it shares many aspects of purely conceptual models and is backed by field evidence, its quantitative basis places it into the realm of analytical models.
The conclusions merely summarize earlier work (mainly Palmer, 1981, 1991). Solutional enlargement of caves and other karst features is highly selective in water that is close to equilibrium with dissolved carbonate minerals, enlarging only the most favorable openings – i.e. those that transmit the greatest discharge. This is characteristic of long flow paths within a typical karst aquifer. In contrast, solutional enlargement will be rather uniform along many competing flow paths where there is (1) high discharge, (2) sustained steep hydraulic gradients, (3) short flow paths, or (4) local renewal of aggressiveness by mixing, oxidation of sulfides, etc. These conditions produce maze caves and epikarstic networks. In general, this condition prevails if Q/rL > 0.001 cm/sec (tubes), or /bL > 0.001 cm/sec (fissures), where Q = discharge, r = tube radius, b = long dimension of fissure cross section, and L = distance of flow from where the initial aggressive solution comes in contact with the carbonate rock.