Bozkov Dolomite Caves - Natural conditions
GEOLOGICAL DEVELOPMENT OF THE AREA
The complicated geological development of the Krkonoše Mountains and their foothills, i.e. the area geologically called the Krkonoše-Jizera crystalline unit, can be observed approximately since the end of the Proterozoic, i.e. within approximately 540 million years. At that time and in the following period of the Early Paleozoic (in the Cambrian, Ordovician, Silurian and maybe even in the Devonian period) the area was a part of an extensive marine basin, where mighty formations of clayey and sandy rocks were deposited. Due to favourable conditions of a clean and warm sea, large colonies of corals and other animals also developed, and layers of carbonate rocks were gradually formed from their accumulated calcareous shells. The sedimentation was sometimes accompanied by submarine volcanism with eruptions of lava and accumulation of volcanic ash.
This marine period ended about 350 million years ago with the beginning of the Variscan folding. During that process, firstly the newly-formed rock complexes descended into larger depths of the Earth's crust, where their thermal and pressure conversion (metamorphosis) occurred and secondly they were re-elevated due to orogenic processes. At the end of this restless period, granite magma penetrated from the depth into the folded rocks and formed the Krkonoše-Jizera granite pluton.
The high mountain chain of metamorphic rocks was very quickly and intensely disrupted in the following periods. Already in the Carboniferous period, near the southern edge of this chain the lake basin was formed in the foothills of the Krkonoše Mountains, where gravel and later even sand and mud carried from the surroundings were deposited on the folded crystalline basement. In the following Permian period, this sedimentation was also accompanied by eruptions of so-called melaphyre lavas. Numerous volcanic bodies with occurrences of gemstones in the Krkonoše foothills were left after them.
After a long period of continental development, the last marine flooding occurred in the Late Cretaceous. During the Mesozoic time, a several-hundred-metre-thick formation of sandstones and other fine-grained sediments was deposited on the flat bottom of the Cretaceous sea. After the Cretaceous sea dereliction, the area remained flat without higher differences in elevation. Changes were caused in this relief as recently as the intense Alpine folding, which took place in the Tertiary Paleogene south and east of the Bohemian Massif. The northern part of the Krkonoše-Jizera crystalline unit was elevated along deep fault lines by more than 1,000 m forming the basis of today's ridges of the Krkonoše Mountains. Renewed volcanic activity with outbursts of basic lava gave rise to outstanding view points, e.g. the Kozákov Hill or the Trosky Castle ruins. At that time also the present network of watercourses gradually cutting into the base and forming today's deep valleys began to be formed. This way, step by step, bodies of limestone rocks of future karst islets were uncovered, and thus the formation of caves and other karst phenomena was enabled.
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EXAMPLES OF CONVERSION (METAMORPHOSIS) OF ROCKS |
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shale → phyllite |
HYDROLOGYBIOLOGY OF THE CAVES
The Bozkov Caves do not exactly have typical karst hydrography – they are not caves where water flows in underground beds or tubes and then bursts to the surface with a mighty karst outflow. We can find perfectly still underground lakes here with blue-green water surfaces rippled only by falling water drops. The uniform water surface of all underground lakes is at the level of 440 m a.s.l. and water fully fills all lower situated cavities.
The deepest point known so far is 14.5 m below the water surface. Water from the cave system flows through little known routes to the surface debris, where it springs forth through so-called Kramář exsurgence with a spring-discharge of 1.2–1.5 l/s and flows out to the Bozkov Brook. Although water enlivens the guided tour through the caves, it is a big problem for surveys and possible new discoveries. That is why the water level was artificially reduced as early as at the beginning of the Bozkov Caves survey in 1959. Initially the water was pumped from the caves; later the water level was permanently reduced by 5 m by a technical arrangement. In light of this fact, it was later possible to open the cave in the present extent.
Both the results of hydrological measurements and of water analyses confirm that underground lakes are fed not only by precipitations falling on the surface of the dolomite body, but also by waters flowing from fissures of surrounding non-karstic rocks, particularly phyllites.
There are no known important paleontological findings from the Bozkov Dolomite Caves. That doesn't mean, however, that there are no living animals in these spaces. But there are only a few of them that can be seen.
Probably the most important representative of fauna adapted to life under the earth is a small colourless crustacean of the Niphargus genus that lives in the waters of the underground lake.
Among xerophilous animals, especially representatives of the insect kingdom – springtails, diplurans and beetles of the Catops, Oiceoptoma and Pterostichus genera appear in the caves. They are all small animals that can hardly be seen by the naked eye. Animals that exploit the cave environment only for a temporary time are much more notable and known. The Bozkov Caves are also home to various species of flies, butterflies, beetles and spiders dwelling predominantly in the entrance space.
The most popular animals that live under the ground are bats. They use the caves as a hiding place in the winter season, where they hang upside down or are hidden in crannies and spend most of the winter hibernating there. Their numbers in the Bozkov Caves are not high and bats do not form colonies here. The most frequent is the greater mouse-eared bat, but the brown big-eared bat, Daubenton's bat, the barbastelle bat and the lesser horseshoe bat have also been found here.
Plants do not grow in natural caves, since there is no light and therefore no photosynthesis. Plants in the form of seeds get into the caves that are open to the public, such as the Bozkov Caves, mostly with the flow of air, but they can germinate and survive only in places with enough light. This is how mostly lower plants like algae, fungi, mosses and ferns called “lampenflora” appear in the vicinity of some reflectors. They are a recognised problem in commercial caves, so they are, already in the primary stage, periodically removed from the whole route of the Bozkov Caves. The only place where they are intentionally left for didactic purposes is the so-called Mechová zahrádka (Moss Garden) in the cave Za Prahem (Beyond the Threshold Cave).
BIOLOGY OF THE CAVES
There are no known important paleontological findings from the Bozkov Dolomite Caves. That doesn't mean, however, that there are no living animals in these spaces. But there are only a few of them that can be seen.
Probably the most important representative of fauna adapted to life under the earth is a small colourless crustacean of the Niphargus genus that lives in the waters of the underground lake.
Among xerophilous animals, especially representatives of the insect kingdom – springtails, diplurans and beetles of the Catops, Oiceoptoma and Pterostichus genera appear in the caves. They are all small animals that can hardly be seen by the naked eye. Animals that exploit the cave environment only for a temporary time are much more notable and known. The Bozkov Caves are also home to various species of flies, butterflies, beetles and spiders dwelling predominantly in the entrance space.
The most popular animals that live under the ground are bats. They use the caves as a hiding place in the winter season, where they hang upside down or are hidden in crannies and spend most of the winter hibernating there. Their numbers in the Bozkov Caves are not high and bats do not form colonies here. The most frequent is the greater mouse-eared bat, but the brown big-eared bat, Daubenton's bat, the barbastelle bat and the lesser horseshoe bat have also been found here.
Plants do not grow in natural caves, since there is no light and therefore no photosynthesis. Plants in the form of seeds get into the caves that are open to the public, such as the Bozkov Caves, mostly with the flow of air, but they can germinate and survive only in places with enough light. This is how mostly lower plants like algae, fungi, mosses and ferns called “lampenflora” appear in the vicinity of some reflectors. They are a recognised problem in commercial caves, so they are, already in the primary stage, periodically removed from the whole route of the Bozkov Caves. The only place where they are intentionally left for didactic purposes is the so-called Mechová zahrádka (Moss Garden) in the cave Za Prahem (Beyond the Threshold Cave).