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The underground world of karst: Speleogenesis


Speleogenesis is the complex process of the creation and development of speleological structures, and part of the overall process of karstification.

Speleogenesis results in the creation of speleological structures of different shape and internal morphology, which is encompassed by the term speleomorphology. Both speleogenesis and speleomorphology are part of geospeleology, a branch of speleology that studies the form and creation of speleological structures in karst and sediments within them, and the climatology, hydrology and geophysics of the underground.

The process of speleogenesis, and with it the formation and evolution of karst, requires three fundamental conditions: soluble rock, secondary porosity, and the presence of water. The main geomorphological process in which water has a destructive effect on rock is corrosion.

The course of speleogenesis can be tracked through several phases. Speleogenesis begins with the exposure of soluble rock to atmospheric influences. In addition to surface corrosion, run off water from the atmosphere trickles in through the cracks, corroding the rocks. This process is very slow. When the water penetrates a path from the entrance to an exit from the karst system (spring), the fissures take on the function of a karst conduit. Water begins to flow more quickly through these fissures, expanding it, though this still does not create a cave. Further expansion of the fissure, due to the increased denudation of the rock walls, turns the fissures into a channel. Expanding the channel increases water flow, and the corrosion process is further amplified by fluvial erosion, as the process of mechanical crushing and carrying rock particles by the water flow. Changes in the position of the erosion base and water levels have a strong effect on the process of speleogenesis. A lowering of the water level results in the cutting of a canyon, while a rise in water levels increases denudation of the channel ceiling, forming different types of grooves. This process is called paragenesis. Long-lasting reductions in the level of the erosion base creates multi-layer channels, and results in the cave in and formation of speleothems in channels above the level of water flow. The final phase in the development of speleological structures begins when they lose their hydrogeological function. Cave areas begin to fill in more with speleothems. Following the surface karst denudation, the level of the surface also lowers and may cause unstable cave ceilings to cave in in places, and the entire cave channel can cave in, creating a ceilingless cave. It is important to stress that the tectonic, hydrogeological and lithological properties of the rock, the geomorphological processes, climate change, changing sea levels and more can have significant modification impacts on this process.

In Krka National Park, the speleological structures were formed in various types of geological substrate, with the exception of flysch and dolomite deposits. Most structures were formed within the Promina deposits, conglomerate-marl-limestone systems, and in rudist limestones.

In the Quaternary structures, the formation of speleological structures is tied to the travertine barriers. Though usually of small dimensions, these caves are particularly interesting since they were created in fossil travertine and contain travertine cave ornaments.

To date, 67 speleological structures have been researched in the Krka National Park area.