Comparison between limestone and glacial karst evolution mechanisms

Karst systems in limestone evolve over geological time-scales by dissolution of limestone, driven by water flow through fractures. Glacial karst systems evolve on daily-seasonal time scales, by melt-driven enlargement of conduits and water passages. There are many similarities between the basic mechanisms involved in the development of these two types of karst systems: A positive feedback between increased water flow rates, higher undersaturation, and increased dissolution rates, facilitates conduit growth in karst systems; a positive feedback between increased flow rates and turbulent/viscous heat generation facilitates conduit growth in karst systems. Due to the inherent tendency of these positive feedback mechanisms to amplify differences, both systems are prone to unstable growth patterns that likely explain the formation of discrete passages/shafts/conduits. Both systems often evolve in tensile stress or low stress regimes, where closure of enlarged conduits is weak/slow. There are also some important differences between limestone and glacial karst systems: creep closure is an important process that constrains the growth of glacial karst systems, but is not a factor in limestone karst systems; hydrofracture propagation on short time scales plays an important role in the growth and propagation of glacial karst systems, but is seldom a factor in limestone karst systems. Glacial karst systems are also highly influenced by subtle thermodynamic processes occurring in the neighborhood of the pressure melting point, which varies with pressure. Thus the role of turbulent/viscous dissipation of mechanical energy to produce thermal energy is a uniquely important feature of glacial karst systems. I will present an overview of the fundamental governing equations for the development of limestone (both epigenic and hypogene) and glacial (both temperate and polythermal) karst systems. I also present examples of numerical simulations of prototype limestone and glacial karst evolution and relate simulation results to field observations.