|
|
 |
Selected Publication Alert: |
 |
|
| Gams I. |
| Kras v Sloveniji v prostoru in casu (Karst in Slovenia in space and time) |
| Source: |
| Keywords: karst, Slovenia |
Abstract:
The historical development of the words karra(n) - kras (karst, carso) and regional names Kras - Karst (Carso) is described first. This name kras is still used in some parts of Slovenia and indicates barren, rocky ground, irrespective of whether the rock is limestone or not. The popular name kras can be traced back to the Indo-European (Paleo-European) word karra(n) = stone, from which also the international term Karren and regional names Carniola = Kranjska, Carnia, Carantania developed. In the historical development of the Slovenian language the word changed from karst into kras by the so-called liquid metathesis. This name began to be used by Slovenians who are the autochthonous people of this region, which is the north-western corner of the Dinaric Karst. The region Kras, one third of which is of Italy since the second world war, is situated between the Gulf of Trieste and the Vipava valley. The regional name Kras was introduced into science in the first half of the 19th century as a technical term at the time when the south-eastern Dinaric Karst was part of the Turkish empire where communications were bad and travellers from Middle Europe to Italy had to cross the Karst (Kras). The transformation of the word from a regional name into an international term was in three stages. First, it was recognized that in the Karst region unusual and characteristic phenomena occur. Second, similar or identical features were discovered in adjacent areas. Third, this new term for these features common to all these regions and abroad was introduced.
In the year 1778 the first version of the popular term kras in the form karosh was published by the polimath Balthasar Hacquet living in Carniola. F. Hohenwarth was the first in Slovenia to write, in 1830, on the origin of the term karst which derived from the region Karst, and on the extent of "Karstland" above the Adriatic coast between the river Soca (Isonzo) and southern Greece and some other countries. The characteristics of the region Kras in the professional literature (a bare stony treeless surface with dolines) were first published in the middle of the 19th century in the German language which was at this time the scientific language in Slovenia. Therefore the names Karst (and karst) and not Kras (and kras) prevailed in the world.
The first part of this book is an analysis of the various karst forms in Slovenia where the karst areas total 22270 sq. km (42 % of the state) and are spreading from the Karawanke range and plateaus in the Julian Alps at an altitude of 2500 m to the shore of the Mediterranean Sea. The most prominent karst forms abroad are mentioned too, for comparison. In this part of the book the genesis of the forms underground and on the surface are considered, and foreign and Slovenian authors are cited. Also in Slovenia the most impressive forms appertain to the so-called contact karst forms (i.e. the lithologic contact of karst rocks, in Slovenia recently limestone and some dolomite only, with impermeable or semipermeable sediments, Eocene flysch, Palaeozoik beds and some kinds of dolomite). In this contact are also the most prominent caves - Skocjan and Postojna caves, and the biggest poljes. To the numerous opinions on solution doline development the book adds a new one. It begins as a subsoil doline in the more fractured rock. On two diagrams are shown the speed of solution of different grain sizes of micritic Cretaceous limestone tested in rain water and in acid river water in the laboratory of the Geographical Department of Ljubljana University. The faster solution of the more crumbled limestone is evident in nature, too. The further deepening and widening of the doline is an automatic process as the size of the slope with its solution in the soil/rock interface exceeds the circular opening of the doline top where the basin began to deepen. This excess is increased with increased depth and is greater in the case of bowl-like dolines than of funnel-like dolines. The bowl-like cross-section is for this reason the most common in bigger dolines. The excess is the greatest with the kettle form, a typical form of alpine snow climate. Frost also crumbles the rock in a temperate climate which accelerates the solution of the rock and also of the rubble covered by soil at the bottom of the basin. In the colder phases of the Pleistocene in Slovenia these nival processes extended to the lower karst areas where animals typical for cold steppe predominated. This climate which reduced biological activity was favorable also for genesis of potholes.
The book describes karst valleys (Rakov Skocjan), uvalas (basin of Podpeskojezero) and poljes (Ponikve, Globodol, Planinsko polje) as basins which could not develop by normal karst processes only. The only possible explanation is tectonic sinking. The general direction of the overall outflow from the Dinaric Karst is controlled by younger, mostly Quaternary tectonic sinking in the border regions of the Dinaric Karst. It is oriented to the Friuli plain (and the Gulf of Trieste), Quarnero gulf, Karlovac, Krka and Ljubljana basins, and to Ljubljana Marsh (Ljubljan-sko barje) in particular.
The analysis of the karst regions in Slovenia and the karst features in them occupies the second part of the book. Regions are divided mostly according to the age of Neogene and Quaternary karst processes after erosion has exposed the karst surface from impermeable cover. Nearly one half of Slovenia (between the Austrian and Croatian border and the line Kranj-Ljubljana-Ra-dece-Novo mesto) is partially still covered by remains of the Miocene impermeable sediments. There the karst is younger, the karst areas are isolated and karst forms are rare. Karst there is limited mainly to the isolated Mezozoic limestone and dolomite patches. In the hilly land of north-eastern Slovenia dry valleys, a few dolines, blind valleys, little caves and springs are developed also in Miocene limestone and carbonate sandstones. Three caves are open to tourists there. The most visited is the cave Pekel in the Savinja valley (Celje basin). At the entrance into the cave Zeieznajama near Domzale is a speleological museum. Also in this part of Slovenia many caves were used by paleolithic man for shelters. The karst in the Prealpine Mountains extending from the Croatian border to the Italian border south of the Julian Alps is limited to Mezozoic limestone and dolomite. The greatest karst areas outside the Dinaric Karst are in the Julian and Kamnik-Savinja Alps. The higher and smaller barren plateaus in Mts Kanin, Komna and the Valley of' Triglav lakes in the Julian Alps and in eastern Kamnik-Savinja Alps display mostly limestone pavements, snow kettles, shafts excavated by water of melting Pleistocene glaciers, and melted snow. Cavers in the last two decades have explored on the plateaus five shafts with depths over 1000 m. Four of them are on the plateaus Kanin - Rombon (Cehi II, deep -1533 m, Crnelsko brezno,-1198, Vandima,- 1182 m, Rene shaft, -1003 m), and one in the eastern Kamnik-Savinja Alps (System Molicka pec, -1130 m). Stony high alpine karst forms are denser mostly in the isolated plateaus (of mountains Kanin, Krn, Triglav, Kriz, Komna, Skuta) and they are the largest in the forested eastern Julian and Kamnik Alps (Mezakia, Pokljuka,Jelovica, Veza), where Pleistocene glacial and periglacial sediments filled many karst depressions. In the western Julian Alps is the cave Poloska jama 704 m deep and 10800 m long. On Mt Kanin (2587 m) the shaft Vrtoglavica (-643 m) has a 603 m deep vertical section and is now probably the deepest shaft of this kind in the world. In these caves and elsewhere under the rocky surface the percolation water as a rule does not deposit flowstone. Its total hardness lies usually below 110 mg CaCO3/l; in the lower karst (1500-800 m) covered by soil it is usually above 170 mg, in the region Karst and in low karst plains (Bela Krajina) above 220 mg/1. In the stony alpine karst the solution front (the contact of aggressive and dripstone forming water) is up to 1000 m deep and in the lower covered karst less than 3-10 m below the surface.
In contrast to the Julian and Kamnik-Savinja Alps where limestone occupies two thirds of the area, in the Mt Karavanke the carbonate rocks are less than one half of the surface. At an altitude of 1700 m there is the famous Slovenian paleolithic cave Potocka zijalka with deposits of sand presumably derived from the Miocene sediments which covered the Olseva mountain many million years ago. Also the cave Sneznajama (Snow Cave) at an altitude of 1600 m on Mt Raduha (2062 m) is older than the mountain uplift to the present altitude. In the Holocene the rivers in the lower karst are rapidly depositing travertine on the surface and flowstone in the caves if the water is highly saturated with calcium, magnesium and sulphate.
The Dinaric Karst is the largest connected karst area in Slovenia stretching from the Prealpine mountains to the Istria Peninsula in the S and into Croatia; it represents about 2/3 of all karst land in Slovenia. In the SW larger patches of the impermeable Eocene flysch cover remain. The rest of the karst in Notranjska and Dolenjska is without them and it is the oldest karst in Slovenia. The general characteristic of the whole Dinaric Karst system situated between the Isonzo (Soca) river and Mts Prokletije in Albany, as a karst of dolines and poljes, is valid also for the Slovenian Dinaric Karst. On the coastal lowland of Istria the dolines are rare or absent, but are dense at higher elevations with a colder Pleistocene climate where on the mountains Notranjski Sneznik (1796 m) and Golaki (1495 m); glaciers left large deep dolines and deep potholes. On mountains with a more stony surface forest prevails as a consequence of soil erosion in the colder Pleistocene climates. The deep reddish Neogene soil cover dated by geologists as Plio-Quaternary deposits remained locally in the submediterranean region Kras and in the low eastern rim of the continental Dinaric Karst in Dolenjska and the low karst plain in Bela Krajina. In the higher and humid continental Dinaric Karst the Neogene and Quaternary processes left in the Notranjska and high Dolenjska regions poljes, dolines and long water caves. The Triassic dolomite, which predominates on the north-eastern rim of the Dinaric Karst, is semi-permeable bearing a hill and valley landscape of fluviokarst. In Notranjsko podolje ("dry valley") in the limestone between two dolomitic belts the karst water level remained near to the bottoms of the poljes of Babno polje, Loz and Cerknica, and before and after a dam built of dolomite (Planina). The bottoms of the poljes Ribnica, Koceyje, Dobrepolje, Globodol and Grosuplje have been levelled before the valleys of the rivers Kolpa, Krka and Temenica sank, the first two in canyons. The most famous of them is the polje-lake of Cerknica with a periodical lake (up to 26 sq km of water surface). At the end of the 16th century, the polymath J. V. Valvasor was elected member of the English Royal Society for his explanation of the lake filling and empting by means of lakes in mountains, connected by siphons. The river Ljubljanica flowed on the surface before the Quaternary in the wide, graben-like dry valley called Notranjsko podolje. There the water caves are situated near the surface which made collapsing of their ceilings (to form collapse dolines) easier (as in the karst valley of Rakov Skocjan at the lowest point of the tectonically sunken uvala). In about 300 sq km of karst land between the poljes of Postojna, Bloke, Loz, Cerknica, and Planina the inflow and outflow caves more than 2 km in length total 70 km. Two of them, Kriznajama (8,163 km, with lakes behind the recently forming flowstone barriers) and Planina cave (6,156 km) are open for tourists with guides available in the neighbouring villages.
In the SW part of the Dinaric Karst, now in the sub-Mediterranean climate, many karst features were generated at the contact of impermeable Eocene flysch with Mezozoic limestone. The flysch was tectonically partially overthrust by the older sediment cover, mostly in the western part of the so-called High border plateaus (Banjsice, Trnovski gozd, Nanos, Javorniki, Notranjski Sneznik) which extend at altitudes from 700 to 1500 m from Isonzo valley to Mt Sneznik. The Pleistocene glaciers on the Mt Golaki and Notranjski Sneznik and periglacial climate around them left dense deep potholes. With collapse of the cave roof, the Great Ice Cave Velika Paradana opened to the surface at an altitude of 1140 m. In its collapse doline is the internationally known vegetation inversion as a consequence of temperature inversion. The inverted stratification from bottom ice to mixed forest at its top was researched in the year 1905 as one of the first cases in the world. The 8 km long and 400 m deep dry valley of Cepovan on Banjsice plateau was eroded by the river Idrijca before it was captured by the Isonzo river and after the tectonics tore the transverse stratigraphical belts on both sides.
On the contact of Eocene flysch with Mezozoic limestone in the southwestern Slovenia there developed only one polje, that of Postojna. The biggest outflow river Pivka excavated the longest (20 km) cave and the best known tourist cave in Slovenia - Postojna Cave. In its low Pivka branch, in the tunnel between Lepejame and Crnajama, tectonics dislocated the sandy strata. Since 1818 27 million visitors have seen their abundant flowstone formations. The graded floor inclination as a result of the gravel transporting river Pivka made possible the construction of the unique cave railway in the world. Its guide books and scientific research of dripstone forms, cave biota and in earlier time tourists cave equipment made an important contribution to the development of speleotourism and speleology in Central Europe. In the polje of Postojna is the watershed between the drainage area of the 1000 km distant Black Sea and not more than of 50 km distant Gulf of Trieste as a part of the Mediterranean. It is a consequence of the younger approach of the Mediterranean Sea caused by slipping of the Adriatic plate toward the N and NE and lowering of the Friuli plain which attracted rivers from the East from the area between the Idrijca in the N and Mima in Istria in the S. Its tributary Vipava attracted the streams from the NW border of the Postojna polje, too. The sinking rivers at the village Bukovo formed the 13 km long cave system behind the famous castle of Predjama.
The plateau Kras is a karst of dolines, dry valleys, big caves and with a predominant karst plain on the surface which cuts the anticlinorium built of Cretaceous limestone, dolomites and Paleocene and Oligocene limestone. The karst plain is a result of rivers from the northern, southern (the Triest Bay sank in Young Quaternary) and south-eastern flysch area, recently all in a syncline. Alongside the Divaca fault the anticlinorium is broken, its north-eastern part b younger. On the profile Mt Gradisce (741 m) to the village Povir, after the pre-karst phase and erosion of impermeable Eocene flysch cover up to 1900 m of the Paleocene and Cretaceous limestone has been removed from the rising anticline in 34 million years up to the present. During the following tectonic compression of the Karst anticline two series of hills rose, in the north that of Mt Trstelj and in the south along the state border with Italy, that of Mt Volinjak series, which continues over Sezana gate in Tabor hills (see the maps with geomorphological units). Eas; of Sezana the tectonic uplifting was younger, in Divaca Karst the Paleocene remained on the surface and in Mt Brkini the many hundred meters thick Eocene flysch. There the recent river Reka is still forming the 5800 m long Caves of Skocjan. West of Divaca, after Eocene Flysch erosion, the caves were formed to a depth of many hundred meters below the surface of that time. Later they opened to the surface by collapse dolines. The cave walls and cave river sediments derived from Eocene flysch have been uncovered during t construction of the motorway on the route Razdrto-Italy and Razdrto-Koper ("roofless caves"), one of them more than 1 km long. Tectonic shifting of the Italic micro-plate toward N and NE and the lowering of the Friuli plain, also the plateau Karst inclined toward the West. At the end of Wurm the Gulf of Trieste advanced to the Kras southern border. After excavating the great blind valley of Vreme (its volume is 242 million m3) the Reka sinks in the Skocjan Caves at an altitude of 323 m. It flows though the bottom of the pothole Divaska jama, Labodnica (Abisso Trebiciano) at an altitude of 12 m and further on mostly below the sunken western Kras beneath sea level to the Timavo springs. The Caves of Skocjan, known especially for their huge underground river gorge are included in the UNESCO World natural heritage list as the best example of a contact karst cave.
The sinking rivers from surrounding flysch areas excavated in the Kras of Sezana and Divaca the caves of Divaca, Trhlovca, Vilenica and the Gustincic cave, the last discovered in the year 1998. In them are series of large halls, connected with steeper steps. Huge blocks fallen from ceiling and walls and massive dripstones prove great age. Datation of the huge stalagmites and stalactites and flowstone by means of paleomagnetic and Th/U method have proven an age of one million or more years. The caves of Divaca, Vilenica and Dimnice are open to tourists, too.
Mostly due to the de-agrarisation in the last two centuries the percentage of the forests in Karst area increased from a few per cent to more than one half of the surface. Once a notion of stony desert, Kras is recently more and more a symbol of a successful forested land. An intensive forestation is going on also in the karst of Notranjska and Dolenjska outside of poljes and growing central settlements.
Some surface forms in Slovenia are in their development in transition from one hydrological regime to another and with it in transition from one geomorphological type to the another. In the hilly area north of the Slovenian capital Ljubljana the blind valley Planik is normally indeed a blind valley. But at very high water level the stagnant water there drains by the surface outlet and the valley becomes then a pocket valley. The wider part of the valley of the Visnjica NE of the village Muljava (Dolenjska) was once at low water level a blind valley. In modern times man began, in order to use the further river flow for mills and sawmills, to block the new established ponors in the bed of the river Visnjica, and so transformed it into a steady affluent of the river Krka. With this the former occasional blind valley is transformed in the normal valley. The basin of Rakitnica river situated on the rim of the polje of Ribnica, with its spring and ponors, is a normal (closed) karst valley similar to the famous Rakov Skocjan. At very high water a lake in it drains by a higher dry valley on the surface to the standing inundation water of the Ribnica polje. Then the character of karst valley is occasionally lost. The valley at the village Podioz (near Loz) is at very low water stage a dry valley and at higher water stage in its first part a semi-dry valley with a short-term lake in it. At the extreme high water level it is, with its surface tributary to the polje of Loz and its Obrh, a pocket valley.
The cave register of the Slovenian Caving Union and of the Karst Research Institute in Postojna contain in the year 2000 7800 caves; that means a mean density 1 cave in 33 sq km. In the Dinaric Karst it is much higher. In Slovenia, the number of vertical (and subvertical) caves exceeds the horizontal caves, especially in the higher karst. This is considered to be a consequence of the most decisive control of the Pleistocene nival climate on the surface.
The main tourist cave in Slovenia is the Cave of Postojna. It is representative of the continental Dinaric Karst and the Skocjan Caves of the Slovene Littoral Karst. In the Skocjan Caves is the astonishing huge river canyon, and in the Postojna cave the abundant dripstone formation and the longest cave railway in the world. Its construction was possible as the river Pivka in the geological past levelled the main channel with its gravel.
Fourteen caves are open for tourists; in half of them the speleothems are exceptionally rich (compared with the average tourist cave in Europe). The total number of cave tourists in the year 2001 is more one half of a million, three quarters of them came from abroad. |
| Date Published: 2003-12-09 |
|
|
| Pages: 516 |
| Contact E-mail: klim@speleogenesis.info |
<<< Back |
|
|
|
