14 show caves of the Czech Republic: VISITOR RULES IN EFFECT FROM NOVEMBER 22, 2021 More
Agentura ochrany přírody a krajiny České republiky www.nature.cz
Česká informační agentura životního prostředí (CENIA) www.cenia.cz
Česká geologická služba www.geology.cz
Česká inspekce životního prostředí www.cizp.cz
Český hydrometeorologický ústav portal.chmi.cz
Správa jeskyní České republiky www.jeskynecr.cz
Správa Krkonošského národního parku www.krnap.cz
Správa Národního parku a chráněné krajinné oblasti Šumava www.npsumava.cz
Správa Národního parku České Švýcarsko www.npcs.cz
Správa Národního parku Podyjí www.nppodyji.cz
Státní fond životního prostředí České republiky www.sfzp.cz
Výzkumný ústav vodohospodářský T. G. Masaryka www.vuv.cz
Výzkumný ústav Silva Taroucy pro krajinu a okrasné zahradnictví, v.v.i. www.vukoz.cz

Bozkovské Dolomite Caves

Characteristics / Evolution of the Caves

DEVELOPMENT OF THE CAVES

Generally, four main phases of development of the caves can be distinguished: formation, widening, filling and destruction. However, the real process is much more complex; its individual phases blend together and in some cases are even repeated, which is also the case of the Bozkov Dolomite Caves.

In caves, which are our windows to the geological past, the information on the area development is recorded in the courses and shapes of corridors, in layers of their sedimentary fillings, solid products of weathering and in sinter, stalactite and stalagmite formations as well. Phases and courses of geological development are also documented by grooves and polishes on the walls, by cave-ins and fallen down blocks of rock.

During early development stages of the caves microscopic channels formed on the rock joints were widened by water slowly flowing for millions of years to form the current shape of the cave corridors. Indications of primary “proto-caves” were preserved in some parts thanks to the fact that they were filled with oxides of iron and manganese in the form of small branch-like structures – dendrites. In general, dolomites and dolomitic rocks are more resistant to dissolution than limestones, so that caves are not usually formed there. Nevertheless, the extreme aggressiveness of water from crystalline rocks in the surroundings of Bozkov caused formation of the largest cave system in the dolomites of the Czech Republic. Initial forms of the caves were formed deep below the surface and were fully filled with water. After carving of surrounding valleys and a decrease in the groundwater level, areas at higher altitudes remained dry and partly filled with insoluble remains of strongly silificated dolomite. Running atmospheric water gradually carried other solid products of weathering and clays to them, so that a part of the caves was fully filled. Stalactites, stalagmites and sinter coatings covering walls and the surface of older clay fillings are among the youngest formations. Modern methods of dating were successfully used for the determination of the beginning of formation of Bozkov stalactites and stalagmites about 250,000 years ago. Sinter coatings together with stalactites and stalagmites are being formed in the cave to the present day. The youngest are small needles of a rare mineral – aragonite, which occur in several places of inaccessible areas of the caves. During cold Quaternary periods, spaces near the surface were frozen through, which caused mighty breakdowns of ceilings, stalactite decoration dropped off and some spaces were even fully blocked by cave-ins. In other places, on the other hand, the stalactite and stalagmite decoration is being slowly re-dissolved by aggressive water.

SELECTIVE CORROSION

Special rugged shapes of corridors together with their detailed modelling formed by the process of selective corrosion are typical for the Bozkov Caves. Due to strong silification of dolomite, its dissolution could not take place uniformly. Insoluble veins of quartz and even whole layers of quartzite, as well as a dense network of fine quartz fibres that the rock is thick with, were exposed and formed due to water corrosion into the shapes of leaflets, laths, benches and reticular or honeycomb structures of various strengths, which, especially on the walls and ceilings of Nové jeskyně (New Caves), form unique formations. In some places, thicker siliceous layers form solid walls of spaces, limit the width of corridors and dictate their direction (e.g. in Blátivá chodba (Muddy Corridor), in Loupežnická jeskyně (Robber's Cave) and especially in Vánoční jeskyně (Christmas Caves), which are not open to the public).