Unroofed Caves Provide Important Clues to the Karst Development

Abstract

Unroofed caves are old caves that were revealed on account of the lowering of the karst surface. They are preserved by their infill—mostly alluvium and flowstone. It became clear during the motorway construction undertaking in Slovenia that unroofed caves constitute a relatively common karst landform. In fact, more common than karstologists had imagined before the karst surface was uncovered through earthworks. The various types of notches occurring on the surface have long been interpreted as types of dolines or as the result of the lithological properties of rock and its fracturing. 75 km long and, on average, 25 m wide stretch of the motorway across the classical Karst gave up 350 caves, of which 90 are unroofed caves. Some of them make up the same cave system. New findings prompted karstologists to become more aware of these unique surface karst forms. In the process, numerous unroofed caves filled with all types of alluvium were discovered. There were several attempts at typification of the characteristic shapes of unroofed caves and to design partial models to explain their typical formation processes. The surface and subcutaneous dissolution of carbonate rock and its disintegration from back in the Ice Age, brought about the lowering of the karst surface. Old caves, which were formed by erstwhile water flows and are partly intersected by shafts which drain water from the permeable karst surface, pop up as either empty or filled with alluvium. The caves were formed as a part of a system of cavities in a period when impermeable rocks had enclosed the aquifer higher up, causing the underground water in the aquifer to be at a higher level. The hypothesis was that the karst topography and its remarkable systems of valleys can be traced back to former surface water throughflow. However, revealing the surface did not provide the evidence to support this hypothesis, instead obvious signs of former water throughflow in carbonate rock were identified—manifested as open and cut through old caves.