2.4 Summary of Formation of Conduit Flow

In summary, the evolution of karst development is a function of the availability of chemically aggressive water over time. The availability of chemically aggressive water depends on the volume of recharge water and CO₂, as well as varying water table elevation, dissolved and particulate organic content, sulfide mineral content, temperature, and mixing of different waters at depth. Once chemically aggressive water is present at depth, karst openings are enlarged by dissolution of rock surrounding permeable openings which then become more permeable, thus higher flow volume and velocity bring more aggressive water in contact with the soluble rocks and the karstification process proceeds. This is a simplified discussion as the formation and depositional environment of carbonates is complex and results in extreme variability in the resulting rock formations. Post-depositional structural changes may also affect how and where fractures occur that allow aggressive water to begin to move through the rocks. The changing geologic structure and climate over the millennia are collaborators in the creation of the dissolution features.

Coastal karst aquifers form by complex processes involving mechanical weathering, and biological and geochemical processes creating dissolution and formation of sea caves. While seawater is generally saturated with calcite, dissolution occurs under a variety of conditions, and not all the conditions understood (Taborsi and Kazmer, 2013). The extremely complex processes involved in speleogenesis and karst geomorphology occur over geologic time scales, and are not the focus of this book.

Exercise 1 invites the reader to consider the composition of carbonate and evaporite rocks.