Solution pipes and focused vertical water flow: Geomorphology and modelling

Focused flow forms distinctive features termed solution pipes (vertical cylindrical voids) in the epikarst zone of porous calcareous rocks with medium to high matrix porosity. Solution pipes vary in size, but are generally less than 1 m in diameter with variable depths, the deepest reaching 100 m. Most occur in eogenetic rocks, particularly in Quaternary calcareous sandstones (calcarenites), but some pipes are also reported in Miocene-Pliocene and Cretaceous chalk and calcarenites. Most of the published research favours their dissolutional origin, but offers different theories regarding the initial trigger that focused the water flow in the host rock matrix, including vegetation patterns and rock heterogeneities. Here we review the current state of knowledge regarding geomorphology of solution pipes and discuss in greater detail the potential role of dynamic instabilities and self-organisation in the emergence of focusing patterns. We review theoretical and numerical studies which allow estimation of interpipe distances, distribution of pipe lengths, extent of pipe merging and the influence of rock porosity on their shapes. In theory, linking the numerical predictions with field measurements might allow the use of pipe characteristics as potential paleoclimatic indicators, provided the problems of dating can be overcome.