The Karst Between Lešnica and Kronovo, Revealed During the Motorway Construction

Abstract

The earthworks during construction of the motorway section Lešnica–Kronovo revealed a karst surface and a part of the epikarst. Both were most distinctly characterized by their subsoil formations, i.e. the development underneath the thicker layers of alluvia and soil. The water percolating through them intersected the carbonate rocks, limestone, and dolomites into subsoil stone forests and carved out underground cavities. The stone forests expand across the entire surface of the route. Their shape and size mostly depend on the characteristics of the rock. The rock is, in fact, fractured with a more or less thick network of vertical cracks, alongside which the subsoil crevices were carved out by the water. Between them, stone pillars of various sizes have formed. The biggest among these are 10 m wide at the base and reach up to 8 m high. Most are narrower, though. Their long-lasting formation and development are evidenced by their shape which becomes narrower towards the top. Many of them have their tops either pointy or blade-shaped. Thickly fissured limestone intersects into the stone forest as well. Their shape is preserved under the surface. In fact, distinct crevices have formed alongside numerous fissures which criss-cross the rock in various directions. The rock next to them is crumbling. The rock is intersected by subsoil rock forms, i.e. flutes, tubes, notches, and niches. The rock is covered with a layer of weathered rock 1–3 cm thick. The contact between the rock and the alluvium is, in fact, very narrow, so the water does not wash away the melting entirely. The weathered rock surface tends to consolidate during dry periods and remains soft when moist. We tried to analyse such subsoil formation of the rock by conducting laboratory tests on plaster. The cavities in the upper section of the uncovered epikarst zone are underground since, during formation, they are filled with fine-grained alluvium brought from the surface by the water. They can be categorized into underground shafts and smaller caves, formed along more or less gently sloping horizontal or along slightly sloped fissures and bedding planes.