> THE KARST - Evolution and the different types of caves
Evolution of the karst.
One of the formative factors of karsts is the vertical circulation of water, which is closely related to the existence of a “base level” where the water gathers before flowing out of the underground system.
This base level is generally that of the valleys surrounding the limestone formation.
Erosion by surface runoff water deepens the valleys. It will therefore lead to a lowering of this base level, which will revive the circulation of water in the lower parts of the underground system and drawing it away from all those upstream.
A new division of the various areas of the karst system will be established, corresponding to this new classification of the caves.
Conversely, if the base level rises by the surrounding valleys being filled up, then the higher caves will fill with water again, and the established balance of the karst system will be threatened.
The different processes which maintain the karst will therefore be affected very quickly by changes to the external environment.
The Karst will retain the traces of these successive changes and studying them in detail enables us to trace the history of this environment over time.
The different types of caves.
Each area of the karst is characterised by different types of cave.
In the drainage area are the underground rivers. These are generally in the lower parts of the karst, draining the formation horizontally and creating a communication with the outside.
Grottoes and galleries are ancient drains abandoned by water because of a lowering of the base level; they are found in the area of rapid infiltration. The water circulates through them quickly and often spasmodically.
In this same area one finds the system of fissures where slow infiltration occurs. These may well be micro fissures deriving from the initial cracking of the rocks, or else macro fissures which evolve from the smaller ones by as they are enlarged by the process of dissolution.
The swallow-holes and potholes are characteristic of the epikarstic area. They result from the enlargement by dissolution of surface channels, or from the collapse of the roof of an underlying cavern.
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