Thinking of the Bükk mountains we may recall first the white rocks shining out of the wood or the sheer rocky walls surrounding deep valleys. Springs spouting from rocks or caves hiding in the depth of the mountains may also come into our minds.
The geological history of the Bükk started about 240 million years ago when the central part of today's Carpathian Basin was occupied by a stately chain of mountains. After the north-east verge of these mountains had sunk a sea was surging in place of the Bükk for almost 70 million years between the late Carboniferous age and the end of the Triassic period. As a result of this transgression primarily limestone of various colour and stratification formed deposits but to a smaller extent dolomite and sea clay covers are also perceivable.
The major part of the Northern-Bükk is made up of slate originating from the middle Carboniferous period, these are the oldest rocks of the mountain. The most spectacular exposure of this rock can be seen in the slate-quarry of the Bán Valley. On the northern verge of the mountain (around Nagyvisnyó) an amazing exposure of dark coloured bituminous limestone that was formed at the end of the Palaeozoic in the late Permian period can be observed. In these rocks nearly the entire fauna and flora of the warm, shallow seas of the late Palaeozoic is represented: calcareous algae, foraminifera, corals, sea lilies, rotifera, sea urchins, mussels, snails, trilobites.
The central part of the mountain, the High-Bükk, is made up of white, sometimes grey or pink limestone that was formed in the Triassic period of the Mesozoic. Clay-slate layers can also be detected and also a small amount of dolomite and sand-stone. The most impressive occurrence of the thin layers of our early Triassic limestone deposits are the standing devil's ribs in the Ablakoskő Valley or the Leány Valley.
The grey dolomite of the Vár Hill at Felsőtárkány-village was formed in the middle Triassic and serves as habitat for a unique vegetation. The limestone of the plateau was formed in the shallow sea of the middle and late Triassic period. The abundance of thalloid corals confirms that the formation of these rocks took place in a shallow sea.
The sinking of the sea in the late Triassic is demonstrated by the formation of colourful (grey, pink, red) limestone at Répáshuta-village. In the deepening sea bed flint limestone was accumulated (lower part of Lusta Valley, upper part of Szinva Valley, middle part of Hór Valley). The original structure of thin banks and thick lamella has almost disappeared as a result of strong plication and metamorphic foliation. The lamellated structure that can be easily observed today is the result of the loosening and cleavage of the slate layers.
In the Jurassic period of the Mesozoic colourful deep-sea radiolarite and stratified black radiolarian slates (e.g. roofing slate of Lök Valley) formed deposits with a thick hiatus directly over the late Triassic layer. At the end of the period carbonate sediments established themselves between the various slate layers.
A substantial amount of intrusive magmatic and effusive rock can be found among the Mesozoic sedimentary rocks of the Bükk; in the Triassic period mainly porphyrite and diabase, in the Jurassic period mainly gabbro and basalt layers were formed.
In the pass of the Eger Stream between Szarvaskő and Tardos the road cut exhibiting a pillow structure which is characteristic of underwater basalt effusions is extremely spectacular.
In the late Eocene period, after a long period of erosion, overlying sediments were formed. These are missing in the inside of the mountain, we know about only a few shreds in places safe from erosion but on the periphery of the mountain these deposits can be easily observed.
On the southern and eastern verges of the mountain sea sediment layers can be detected which stretch as far as the latest formations of the Pannonian period and can be found over the late Eocene terrestrial layers and limestone layers. At the foot of the Bükk hundreds of meters of rhyolite tuff can be found in these sediment layers. The so called hive rocks in the surroundings of Szomolya, Cserépváralja, Cserépfalu villages are unique forms of the eroded middle and late Miocene rhyolite tuff.
The sediment rocks and fossils of the middle Miocene sea which covered the entire Bükk for a short period of time can be discovered on the peripheries of the mountain (Határ Peak at Nagyvisnyó, gravel pits of the Éger-vaulk at Dédestapolcsány).
The current stage of the development of the Bükk started about 15 million years ago, at the end of the Miocene period. The present appearance was formed by a number of elevations and erosions. By the end of the Pliocene period the gravel sediments and rhyolite tuff covers had eroded in the inside of the Bükk as a result of the wind, precipitation, decay and disintegration; the dominant part of the mountain became an open karst. In the glacial period the slow elevation continued, the destructive activity of external forces became stronger in the mountain that was growing ever higher. The destruction can be recognised most easily at the frontier of the contiguous mass of limestone and the clay slate layers.
Geologic forces and surface erosion produced a great variety of karst forms in the limestone mountains during the millions of years: sumps, caves, deep gorge valleys, lofty rocks.
The least indented, most homogenous part of the mountain is the 800 m high Bükk plateau which is divided into two territories (Great and Little plateau) by the Garadna-stream. The karst formation had special effect on the present appearance of the plateau. The main features of the gently wavy surface are low horsts, dolina in between (and a subgroup: uvala), swallets, potholes, caves. Horsts of tectonic origin (Kiskőhát) and the long, wide, valley-like hollows under the level of the plateau, the valleys (István-lápa Valley, Fehér-kő Valley) are characteristic of the area. Polje receding on the surface of the Great Plateau were formed as a result of structural motions (Nagymező, Fekete-sár). On the verges of the plateau ravine valleys of karstic origin are stretching (Sebesvíz Valley, Teknős Valley).
The horsts towering at the verges of the central Bükk are the most distinctive rocks of the mountain. Beneath the enormous peaks the remains of those caves can be found which confirm that the central Bükk and the Great and Little Plateau were once integral. At the feet of the Tar-rock, the Magos Rock, and the Köpűs Rock, next to the whirlpool caldrons of former cave-streams the lateral galleries of old caves and the eroding recrystalised dripstones still can be observed.
Wonderful phenomena of the mountain are the karr or devil's tilling, the indented, drilled, pierced limestone surface full of recesses. The enrichment of the carbonic acid content of precipitation contributed to the formation of the karrs. On the frontage of horsts and on the crests the karrs make up karren fields which are hardly passable. The karrs can also be found on the walls of dolinas and swallets.
Apart from the frequently appearing lines of dolinas and twin dolinas the only collapse-dolina of the country can be found in the Bükk, in Udvarkô. One can see here most of Hungary's deepest caves (István-lápai Cave, Szepesi Cave, Kiskőháti Clump) and at the verges of the karst most of our blind valleys with swallets, swallet-caves can be observed .
The sump-caves take us to the rich and variegated undersurface world of karst phenomena. 45 of the 853 explored caves are strictly protected. The deepest cave of the country can be found here, the 250 m deep István-lápai Cave which together with the Szepesi Cave and the István Cave at Lillafüred (the latter is open for visitors) belong to the most beautiful karst galleries abounding in dripstones.
The karstwater treasure in the depth of the mountain is the greatest value of the Bükk. It provides more than 1 million people with clear fresh water. As pollution may get into the karst galleries together with the precipitation, karstwater is very sensitive. We must take care of it!
Once the mountain was rich in springs and streams, however today (as a result of the increased exhaustion of drinking water) one can rarely see open-air springs or living streams.
The last stream valley with natural living stream is the Garadna Valley where you can find water any time of the year from the spring to the outlet.
The water output of the springs and the abundance of water of the streams is highly dependent on the precipitation. There are seasonal springs and intermittent drifts which exist only after snowbreak or in a period of high precipitation. The best-known of these springs are the Imó Rock and Vörös Rock springs where the water-spout can be as high as a human for a few days during the spring-snowbreak.
Travertine separates out from the water of streams spouting from the karst springs and forms dames in the stream bed. The water runs across these dams and continues its way through little waterfalls. The algae and mosses living on the steps of the stream bed intensely stimulate the formation of spring-limestone. The Fátyol(veil) Waterfall running across the spring-limestone steps of the Szalajka-stream, the spring-limestone hump built by the waterfall of the Szinva Stream or the Anna Cave at which came to exist in a recess closed by the precipitation of travertine are all well known, but there are nice spring-limestone formations in the Szentléleki- and Sebesvíz Valleys and at the Harica Spring.
Utolsó módosítás: 2014. október 28., 11:37