In ancient times, people used to believe that evil powers lived deep underground. The areas of caves and caverns were steered clear of because nobody wanted to attract bad luck and anger of malicious devilish powers. Only those who had no other solution, with great uncertainty decided to go underground. Highland robbers liked those places and kept their loot there. Ondraszek and many other leaders did not, however, meditate over the real reason for the formation of underground passages and chambers. Today, however, we already know how caves are formed and what they really are.
Caves are underground passages or chambers of different length and depth. The existence of caves is most commonly associated with the karst phenomena. This process takes place in a territory built of carbonate or sulphate rocks and consists in slow dissolution by water of minerals contained in these rocks. Water dissolves, inter alia, minerals such as calcium carbonate (the basic component of limestone rocks), dolomites, gypsum or rock salt. The most popular rock, in which the karst phenomena occur, are, of course, limestones. For chemists, the process of limestone leaching may be presented in the following way:
CaCO3 + H2O + at2 — › Ca (HCO3)2 = > limestone leaching
For people more related with the humanities:
Limestones are made of calcium carbonate (CaCO3). They are very difficult to dissolve in chemically pure water (H2O) but water, which dissolves these rocks, is contaminated with carbon dioxide (CO2) from the atmosphere. In addition, before water gets into the rocks, usually it must permeate through a layer of soil, from which it also takes CO2 contained in decomposing organic remains. The capacity of water enriched in this way to dissolve calcium carbonate is even 300 times higher than that of chemically pure water. As a result of the contact between water containing CO2 and limestone, the above presented reaction takes place which results in the formation of calcium bicarbonate Ca (HCO3)2. Calcium bicarbonate is more easily dissolved than CaCO3 and therefore it may be further transferred from the place of the reaction.
The process of dissolving begins with the expansion of small fissures, which contain a small amount of water. As far as the amount of water increases, the rate of dissolution and thus of expansion of rock caverns, is increased. Flowing water moves within those fissures and creates so-called karst channels. The main channel drains water to the outside, creating a karst spring – springs of that type are called vaucluse springs and are most commonly located in the bottoms of valleys.
Dissolved calcium carbonate may be precipitated again due to, for example, the pressure drop in water transporting it. The change in the conditions causes a decrease in the amount of carbon dioxide in water which results in precipitation of excess calcium carbonate. For this reason, for example, in the vicinity of vaucluse springs, so called calcareous sinter (travertine) may be encountered. The decrease in the amount of carbon dioxide in water may also result from the change in temperature or absorption by plants. Precipitation of calcium carbonate also takes place in caves – many times, it gives rise to incredibly rich and diversified speleothems, where the most common elements are stalagmites, stalactites, columns or draperies.
In the Polish Carpathians, karst caves are found in the territory of the Tatra Mountains and Pieniny Mountains. However, it should be stressed that one of the most beautiful and the most interesting caves of this type is Ochtińska Aragonite Cave in Slovakia.
By contrast, the territory of the Outer Carpathians is not built of rocks subject to the karst process. This area is built of flysch, i.e. alternate sandstones, siltstones and conglomerates. Therefore, karst processes cannot occur here. Caves present in the area of the flysch Carpathians are of completely different origin. Due to the fact that the process of rock dissolution does not contribute to their formation, they are called pseudokarst caves. For their formation, two phenomena are responsible:
- gravitational mass movements, i.e., processes affecting the development of mountain slopes and tops. These are, inter alia: rock slides, landslides and downhill creep
- processes of weathering and erosion of walls of rock outcrops.
During the formation of caves in flysch sediments, the thickness of rock layers is very important. Sandstone layers, in which caves are usually formed, must be thick and highly compact.
In terms of morphology, flysch caves may be divided into two groups:
- fissure caves – usually found on a fissure or the system of fissures, with a length from several meters to several hundred meters. Such caves are formed as a result of such processes as: boulder chokes, local displacements of rock layers, movements of rock blocks, etc. Their appearance may change very quickly.
- cave niches and bedding-plane caves:
- cave niches – small, low, shallow but quite wide forms most often present at the foot of flysch rocks, under rock roofs. They are formed due to erosion of walls of flysch rocks.
- bedding-plane caves – larger, more complex forms with a significant advantage of the width over the height; they are also formed as a result of erosion of flysch layer outcrops.
Flysch caves are characterised by the lack of speleothems (they may occur occasionally in a very poor form).