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Geology and Speleology
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Karst Landscapes

Bare Karst | Covered Karst | Doline or Sink | Dry Valley | Karren | Karst Cave | Karst Lake | Karst Spring | Losing StreamNatural Bridge | Polje | Ponor | Speleothems | Tower Karst | Vorfluter

From Treccano Enciclopedia Italiana:

Carso: Regione compresa, in senso stretto, nelle Alpi Giulie; secondo un’accezione più ampia si estende, discontinuamente, tra queste e le Alpi Dinariche, dalla Carinzia al Montenegro, articolandosi in varie subregioni, che ricadono in territorio italiano (C. Monfalconese, C. Tiestino ), sloveno (Alto C., C. Carniolino), croato (C. Istriano, C. Dalmata), bosniaco e montenegrino. Le forme tipiche sono quelle di altopiani brulli per la quasi assenza di circolazione idrica superficiale, ma intercalati a depressioni dove l’accumulo di residui insolubili e poco permeabili permette la coltivazione e il conseguente insediamento umano. [Estratto da:]

Karst is a geological phenomenon that was first described to be lying in a low plateau completed by a peninsula with cliffs descending sheer to the sea and indented by deep bays - encompassing a part of modern Slovenia and Istria. The ancient name of this region was Carusadius, now called Carso, Kras or Karst, which means rocky place.

Since the the phenonmenon was first described, all areas with a similar geological situation have adopted the name of Karst Areas. In the geographical sense, karst is an arid, stony and infertile territory near Trieste which became known for its extensive and characteristic erosional phenomena and its beautiful stalactitic caves, the result of subterranean erosion. In its geological use the term karst has been extended to cover all areas with similar "karstic" formations and underground watercourses - i.e. in Croatia, the islands and the coastal regions.

The type of erosional forms which the karst takes, depends on many variables: 

  • The mechanical structure and chemical composition of the rock. Common rocks for karst areas all over the world are - 
    • Limestone (calcium carbonate CaCO3)
    • Dolomite (magnesium calcium carbonate CaMg2CO6)
    • Gypsum (CaSO4 + H2O)
  • The local climate and temperature range. 
  • The amount of rainfall. 
  • The amount of vegetation - 
  • The uplift and downlift of the rocks and the hydrogeological situation. 

The basic aspects of karst areas are soluble bedrock, cracks and water. The rain water is able to dissolve small amounts of rock and carry them away. Most rocks are not permeable to water, but sediments have horizontal layers. Additionally, during times of uplift and downlift, the layers got mostly vertical cracks. When water follows the cracks, it dissolves the rock and forms caves and caverns. A more detailed description is given in an article written by the Missouri Geological Society in the following excerpt from their article "Missouri Caves, Karst, and Springs" at 

Karst is formed when rainwater picks up carbon dioxide from the air, and dead plant debris in the soil, then percolates through cracks dissolving the rock. The bedrock becomes saturated with water at some level, and dissolving continues as the water moves sideways along bedding planes (horizontal cracks between rock layers) and joints (or fractures) in the rock itself. These conduits enlarge over time, and move the water, via a combination of gravity and hydraulic pressure, further enlarging the conduits through a combination of solution and abrasion of water on the surrounding rock.

Eventually, much of this water under pressure reaches the surface of the land as a spring. A spring may emerge high on a cliff, at the base of one, or even forced upward from below the level of the surrounding surface streams, depending on nature of the surrounding rock, and the altitude of the groundwater level, with respect to the base level of the controlling stream in a drainage area. Often in Missouri, springs have little relationship to surface drainage, because so much of our water movement is actually groundwater movement. In some areas of the Ozarks, more than 70% of all water goes underground via karst processes.

As groundwater levels in an area drop, more and more of the underground passage becomes air filled. When it is sufficiently air filled, springs become cave entrances, passable by humans. Other voids never develop a natural opening, and are intersected by drilling, notably of wells looking for water. At this point, due to changes in chemical equilibrium underground, the resulting caves begin to fill with dissolved mineral, called cave deposits or speleothems. Caves may refill with water or continue to dry out, or even cycle several times as water levels change.

Erosion continues underground, and eventually a cave hollows enough for the roof to thin, and the cave collapses. Such cave collapse may actually unroof the cave if it is near enough to the surface, or simply form a slump in the level of the land. In either example, a sink[hole] forms. Natural bridges and tunnels can be formed as resistant remnants of a cave collapse, or independently, if a block of bedrock becomes cut off from the main land mass, and it is hollowed out by wind, ice wedging, and rain.

Many karst areas have poor soil, and do not retain water easily, allowing it to go directly underground. Sinks also act as "swallow holes" for rainwater; some sinks take water under certain conditions, and resurge it at others. These reversible sinks, called estavelles, are among the curiosities of karst. Some springs in the Ozarks are periodic, or "ebb and flow" springs, whose discharge can be measured to rise and fall independent of local rainfall. Many theories, but no one knows why, for sure. Another oddity of Missouri karst is the karst window, where one may look into a cave or water filled sink below, but getting down there is another matter entirely.

Karst makes for beautiful scenery, but it is very vulnerable to groundwater pollution, due to ease of water flow. Natural filtration is nearly non-existent in karst. To make matters worse, the use of cave conduits as natural sewer lines, and sinkholes as garbage dumps in small towns and rural areas puts the local drinking water supplies at risk. It is only recently that these problems are being addressed. Urban expansion in karst areas often means the building of houses on land which cannot support them and problems with septic tanks, underground pipeline breaks and landfills. 

How a karstic landscape develops

Although the various karstic processes can take place relatively rapidly, karst formation is a long-continued operation, the destructive effects of which have been by no means halted by sporadic programs of reforestation and landscape protection.

Rainwater finds its way through the cracks and crevices typical of porous limestones into the underlying rock, and the carbon dioxide contained in the water converts the solid limestone (calcium carbonate) by a chemical process into dissolved bicarbonate. The dissolved substance is then washed away, and as a result the original hair-line cracks in the rock are steadily enlarged and widened. This then produces a pattern of clefts and ridges, usually running parallel to one another. When a large area is covered with formations of this kind it is known as a karrenfeld or "pavement".

The rainwater can now penetrate even deeper into the ground, forming cavities by the chemical process of corrosion and filling them. Then, when the water begins to flow through these underground cavities, it continues its destructive action in breaking down and carrying away the rock by the mechanical process of erosion.

The water accumulating under the surface forms watercourses and currents in the same way as water on the surface. Recent research has shown, however, that the direction and speed of flow are not determine solely by gradients. in a system of linked cavities, crevices and channels pressure can build up, forming "pressure dams" which can occasionally cause water to flow uphill.

In this way subsurface watercourses develop consisting of caverns, passages and conduits; and the faster the water flows the deeper it cuts its way down. When an underground cavern is not completely filled with water the process of stalactite formation may begin, depending on the rate at which water percolates through the roof of the cavern. If the land above the cavern is covered with woodland the flow of water with a high carbon dioxide content is much stronger than under pastureland or a completely bare surface.

Features of Karst Areas

Bare Karst | Covered Karst | Doline or sink | Dry Valley | Karren | Karst Cave | Karst Lake | Karst Spring | Losing Stream Natural Bridge | Polje | Ponor | Speleothems | Tower Karst | Vorfluter

Definitions [expand]: 

  • A spring is a natural resurgence of groundwater, usually along a hillside or from a valley floor.
  • A cave is an airfilled underground void, large enough to be examined in some way by man.
  • A doline, sinkhole or sink is a collapsed portion of bedrock above a void. Sinks may be a sheer vertical opening into a cave, or a shallow depression of many acres.
  • A losing stream is one with a bed with allows water to flow directly into the groundwater system.
  • A natural bridge or tunnel is a void beneath still standing bedrock, usually of short extent, and allowing human passage from one end to the other, at least part of the time. A natural bridge is somewhat shorter than a tunnel, and is more inclined to be air filled than partly water filled.
  • A polje is a large closed depression draining underground, with a flat floor across which there may be an intermittent or perennial stream. 

Bare Karst

English: Open karst
German: Nackter Karst (r)
Spanish: karst (m) expuesto; karst (m) desnudo
French: karst barré (m+adj); karst nu (m+adj)
Italian: Carso nudo?
Portuguese: afloramento; carste desnudo; carste exposto

Geologists call areas as bare karst because of the lack of vegetation. The bare karst has no rivers and no trees, but the flora is often very interesting. In most cases the bare karst is an artificial landscape, created by men. When the area gets riverless because of the low ground water table, a natural vegetation of forest is able to keep the former state. But as soon as this difficult situation is disturbed by mankind, an irreversible process starts which leads to the bare karst condition. 

Uncovered karst is found on islands and the immediate coastal area of Croatia. The hills and hillsides, now bare, were not always without vegetation. The present barrenness has been brought about by uncontrolled deforestation, the destruction of large areas of woodland to provide firewood, by the failure to replant trees, and the use of the treeless land as grazing for sheep and goats, and with all the consequences in the form of erosion that then followed. In Slovenia this process began more than 2000 years ago when the Romans started to use the enormous trees as masts for their ships. From this point of view, the landscape is a remain of the wars against Carthage. It was also furthered by the Venetians who needed timber for their large fleets and the piles on which their city was built. 

Impressive Bare Karst areas in Europe include:

  • The Triestine and Dinarian Karst in Italy and Slovenia, a single karst area divided into two parts by a political border. 
  • Burren in Ireland. 
  • Gottesackerplateau in Germany. 

Covered Karst

This form of karst is found mainly in the coastal hinterland. Here the limestone rock has often been overlaid by the products of its own weathering and decomposition, and the karstic processes have then continued under the covering of humus. With sufficient rain, trees can grow - oak to about 2600 ft/ 800 m, then conifers to 5900 ft/1800 m, occasionally even higher.

Skocjanske Jame entrance
The entrance to Škocjanske Jame in Slovenia is located in a green dolina, a few hundred meters from Škocjan. An artificial tunnel at the bottom leads to the rear end of the cave. Photo by © Jochen Duckeck 
  1. In covered Karst, the vegetation covers the limestone. This has two important effects on the geology:
  2. The vegetation produces CO2 in the earth, which fastens the corrosion (dissolution) of limestone. The growth of caves is faster than in bare karst. On the other hand, the vegetation covers the limestone from the air, so there is much less erosion depending on weather, e.g., in covered karst no frost erosion appears. 

It is rather difficult to see if a certain area is a karst region when it is a covered Karst area. But if you know the signs, it is easy to recognize with the following questions:

  • Are there caves?
  • Are limestone or dolostone rocks visible, maybe exposted at the valley of a river? 
  • Are there many springs around? (This one is not a sure sign, but a good hint) 
  • Are there any rivers? Large areas without rivers are always some sort of Karst. You will often be able to spot riverless areas on a good map.

Karst areas have a typical soil and vegetation. There is no ground water, so there will be no vegetation that depends on it. The soil may regularily dry, so the vegetation will be used to this and be able to store some water.

The soil is formed by the residuals of limestone dissolution, which are silt minerals. If there is any iron in the limestone, which is rather common, the soil will first have the colour of the iron oxide. But there are two different chemical reactions, depending on the temperature. In tropical and subtropical climates, the colour is red (terra rossa). In colder climates the colour is beige, a very typical yellowish brown. 

Doline - Dolina - Sink - Sinkhole - Cenote - Swallow Hole - Ponor

A sinkhole or sink is a collapsed portion of bedrock above a void. Sinks may be a sheer vertical opening into a cave, or a shallow depression of many acres. In karst areas, a doline, sink or sinkhole is a closed depression draining underground. It can be cylindrical, conical, bowl-shaped or dish-shaped. The diameter ranges from a few to many hundreds of metres. The name doline comes from dolina, the Slovenian word for this very common feature. So this was originally a Slovenian slang word. There are two different mechanisms for the forming of dolines:

  • solution
    The corrosive solution of limestone by rainwater is very high in the area fo crack, allowing the water to run into the rock. This normally forms the bowlshaped type of dolines.

    The solution produces large amouts of clay (depending on the pureness of the limestone). This clay is water resistant and sometimes plugs the drainage, so little lakes of rain water can sometimes be found in dolines, a rare thing in waterless karst areas.

  • collapse
    When a cave grows, there may be a point where the roof of a cavern is not stable enough. This results in (several) collapses that shape the roof like a dome. This process runs out, when the shape is able to hold the weight of overlying rocks.

    If the impact of this collapse reaches the surface, if the overlying layers are too thin. The ceiling collapses and a doline is formed. The doline is often a natural entrance to the cave.

A ponor or swallow hole swallows the water of a stream or lake.


A vegetable patch between Trviž (Terviso) and Beram/ (Vermo). 

A soccer field near Vizinada.

A cenote is a partly water-filled, wall-sided doline. It is formed by the collapse of a cave which is (today, not necessarily at the time of the collapse) filled with water. This sort of doline is very common in Yucatan, México, where a large cave system with many entrances is filled with water. The system was formed during the ice ages, when the surface of the sea was 100 m lower than today. When the glaciers melted and the sea level rose, the caves were filled with water. 

[Where are the cenote in Istria?]

Dry Valley

Valleys without a surface stream are very common in karst areas. They were formed in two ways:

  1. In times before the water table was too deep, the water drained on the surface.
  2. During the Ice Ages, the ground was frozen for several meters below the surface. Summer was too short to melt it this deep. But the frozen ground is water resistant, all cracks are filled with ice. So the drainage happened on the surface. 

Karren - Lapies - Limestone Pavements

Karren are minor forms of karst due to solution of rock on the surface or underground. The name Karren is German, originally it described this feature in the German and Austrian Alps, where exist large karst areas with Karren. 

Karren can be found on any kind of surface. They are formed when water runs down a slope dissolving the rock. Thus karren can be found on any soluble rock like limestone, dolomite or gypsum. Karren always show how the water flows, they run down the slope in the same path as the water. They get deeper and deeper. Sometimes only thin limestone walls, a few centimeter thick, remain.

Very similar dissolution effects produce limestone pavements. They look very similar to karren, but normally they are formed along a crack in the limestone. In this case the water enters the crack and does not stay on the surface. The dissolution continues inside the crack, which gets wider and wider. 

Large limestone surfaces get cut into pavements. The number, position and direction of the clefts depends on the cracks of the limestone. Often the cracks, formed by tectonic forces, run in very few directions. Each direction shows one stage in the tectonic history of the limestone. Limestone with two main directions of cracks, with an angel of about 90° in between, makes the typical limestone pavement which looks like an enormous chess board.

Karst Lake

At first look, karst lakes look like any other lake, but there often is something special with such lakes.

There may be no visible stream flowing in, or none flowing out of the lake. Sometimes there is neither. Those lakes tend to grow and shrink. The water level rises in spring, when the snow melts or after heavy rains. The level falls in dry periods. Some of those lakes disappear completely. Then they are called seasonal lakes, as they only exist in some seasons.

The explanation of all this strange behavour are caves. The lake is fed by springs  below the water level and emptied by swallow holes, also below the water level. Often the same cave works as spring and swallow hole, depending on the season.  Another way to interpret this situation, is to say, the lake is a part of the ground water. The surface of the lake is the water table. When the water table in the hills around a depression rises above the ground of the depression, it is filled with water. When the ground water lowers, the lake dries up. 

It is pretty difficult to decide, if a lake is true karst lake. The geological examination is very difficult and for some lakes the oppinions differ. Missing rivers in and out of the lake, are visible on a map, and give a first hint. Not all seasonal lakes are karst lakes but this is a second hint. And of course the existence of karst around the lake is necessary.

Cerknisko Jezero in Slovenija is a Karst Lake. [Was Čepić lake/lago d'Arsa a karst lake?]

Karst Spring

A spring is a natural resurgence of groundwater, usually along a hillside or from a valley floor. Springs in karst areas differ from normal springs: they normally have a much higher production, as they are just the end of a waterfilled caves system. Also they are highly dependent on the weather. Every rain and, of course, the snow melting leads to increasing production. Karst springs regularly fall dry in dry periods in the summer! On the other hand, the water quality is often poor! Both effects have the same reason: the water flows rather fast through cave systems, there is not enough time for micro organisms to clean the water. So karst springs are not a good source for water supply.

An intermitting spring is a spring that falls dry several times or most of the year.  In most cases this springs are situated above, but near to the groundwater table. As the groundwater table moves inside the rock over the year, it sometimes reaches the spring and the water starts to flow.  As very wet years often resulted in crop failure, the production of some wells were counted as a bad omen. The Hungerbrunnen (famine well) in Germany is an example.

[Where are the karst springs in Istria?]

Losing Stream

A losing stream is one with a bed, which allows water to flow directly into the groundwater system. A very famous losing stream in Germany is the Danube. The Danube-spring is located in the Schwarzwald (Black Forest), from where the Danube flows to the east. Near Immendingen and again near Fridingen swallow holes in the bed of the river make the river loose some water. In dry years, the Danube gets completely dry and is reactivated several kilometers away by some tributaries. The water reappears in the Aachtopf.

Natural Bridge or Tunnel 

This term refers to a natural arch, bridge or tunnel which is a void beneath still standing bedrock, usually of short extent, and allowing human passage from one end to the other, at least part of the time.

A natural arch is an arch of rock formed by erosion (weathering).  A natural bridge a bridge of rock spanning a ravine or valley and formed by erosion.  A tunnel is a nearly horizontal cave open at both ends, fairly straight and uniform in cross-section.

Veliki naravni most
Veliki naravni most, a natural bridge in the Rakov National Park near Postojna, Slovenia. Photo by © Jochen Duckeck 

A natural bridge is somewhat shorter than a tunnel. There are two different types of natural bridges/arches depending on their formation. The following explanation focuses on the second type of natural bridges:

  1. Natural bridges and arches - like in Arches NP in USA - are formed by multiple erosive processes, like fluvial erosion (flowing water, rivers), frost erosion and wind erosion. They may be formed in not soluble rocks like basalt or sandstone, but also in limestone.
  2. Natural bridges and tunnels in karst areas are the ruins of caves.

In large cave systems collapses are very common. Very often they result in domes that are optimal to stand the pressure of the overlaying rocks. Sometimes the caves are large and very near to the surface, so the ceilling gets too thin and collapses. As erosion goes on, the collapsed rooms are widened to small valley with a river, the former subterranean river. The valleys grow larger, the connecting cave remains get shorter. Sometimes the remaining caves are short enough, to see the other end and the next valley. This may be the time to call them tunnel.

Examples of Natural Bridges:

  • Veliki naravni most (photograph above, right) in Rakov Škocjan Nature Reserve near Postojna, Slovenia.

Polje (Karstic fields)

A polje is a large closed depression draining underground, with a flat floor across which there may be an intermittent or perennial stream. The polje may be liable to flood and become a lake, and its floor makes a sharp break with parts of surrounding slopes.

Polje is the Slovenian word for "field", which means the flat and very fertile ground of the valleys in Slovenia. In the area around Postojna many valleys show the same characteristics:

Rakov Polje - Rakov National Park, Slovenia
The end of the Rakov Polje in Rakov National Park near Postonja, Slovenia. The river flows down the narrow valley and enters a cave. It is possible to visit the first part of the cave, but the rest is not even explored by speleologists. Some divers explored only a short part of it, then the river became too deep. Photograph © Jochen Duckeck.
  • The valleys are rather small, a few hundred meters wide and up to one or two kilometers long. 
  • The sides of the valleys are rather steep. 
  • Most valleys have a stream flowing from one end to the other. 
  • The stream enters the valley in a karst spring, often the entrance to a cave. 
  • The stream leaves the valley in a Ponor or the entrance to a cave. 
  • And last but not least: the valley has a flat and very fertile ground.

This typical form of a Polje is easy to explain, when the way they were formed is clear. The karst area is drained underground by caves. If the caves are rather near to the surface and rather big too, sometimes the roof collapses and forms a dolina. The stream tht flows through the cave now flows through the Doline and [data missing].

Typical features of poljes are their disappearing rivers. These usually emerge at the edge of a polje and after flowing for some distance disappear into the ground again. After heavy rain, normally occurring at the end of winter, the cavities in the ground may not be able to absorb all the water immediately. This then forms a lake, which may end by covering the whole area of the polje. The peasants therefore always have their houses at the edges of a polje, and if there is a heavy early rainfall in autumn must make haste to get the harvest in before it is covered by the rising flood-water. The passing summer tourist may be surprised to see small boats lying about among dry cornfields; but these serve a useful purpose when the poljes quickly turn into lakes after heavy rain.

A peculiarity of karstic country is the absence of rivers of any length. Along the whole length of the Croatian Adriatic coast only a few above-ground rivers of any size reach the sea - the Dragonja, Mirna and Raša in Istria, the Krka and Čikola at Šibenik, the Cetina at Omi and the Neretva in the Opuzen delta. The water which seeps into the ground re-emerges at the foot of the hills in the form of large karstic springs.

In the extensive karstic region large numbers of caves have been formed by the erosion of water-soluble rock. The total number of caves can only be estimated, but is certainly over 10,000. In Slovenia alone - where the exploration of caves has been most actively pursued - there are more than 3,500, mostly in Triassic, Jurassic and Cretaceous limestones.

Tower Karst - Cockpit Karst - Cone Karst


Tower karst

cockpit karst; conical karst; kegel karst; polygonal karst


Turmkarst (r)

Kegelkarst (r)


Karst de torres

kárst cónico (m)





Carso (sm) a torri

carso (sm) a coni; carso (sm) poligonale


Carste em torre

cárste cônico


Carst (n) de turnuri

carst (n) conic

This category has a spectacular variety of karst landscape, dominated by steep or vertical sided limestone towers (karst towers) or cones. The towers originate as residual cones and are then steepened by water table undercutting from surrounding alluviated plains.

Tower karst, cone karst and cockpit karst are different but rather similar forms of this kind of landscape. There are two different explanations for this kind of landscape, both explaining a certain aspect of the geology. In reality, it seems to be a combination of both:

  1. Tower Karst is typically interpreted as a karst area in a very late stage of development. To explain this we first need a sort of chronology of karst development:
    1. Limestone reaches the surface and gets subject to weathering.
    2. Ground water starts with the solution of limestone and forms first caves. A lower drainage system around the limestone area is necessary for the secons stage: the rivers and lakes leave the surface, drainage of the whole area is underground. This is the "typical" stage of a karst area, which we know well from moderate climate zones.
    3. The limestone caves get bigger and bigger and start to collapse. Cave systems are marked at the surface by daisy chains of dolines. Dolines merge and form poljes.
    4. The cave systems are more or less collapsed. The former poljes grew and grew until they are all connected and again form a net of subaerial valles draining the area. The former limestone plateau is cut into isolated limestone islands.
  2. The formation of the towers is a combination of tectonic uplift and tropical karst erosion. Tectonic uplift matched by karst erosion increases tower heights, as the solution is bigger in the valleys. If uplift is too slow, the towers are dissoluted and shrink, if it exceeds erosional surface lowering, the towers are raised to hillside locations and the landscape is rejuvenated to form a new generation of dolines and cone karst.

Cone and tower karst exist only in sub tropic and tropic climate zones. Both typically exist in in areas with tectonic uplift. In many areas the towers are full of inactive caves at (multiple) higher levels, and with active caves through their bases. There may be alluvial plains between the towers and flat-floored depressions within them.

  • Cockpit karst is the beginning of the development. After cave systems developed, grew and collapsed, the former caves form huge valleys and the limestone inbetween remains as hills.
  • Cone karst is the more common and less spectacular form of this landscapes with steep limestone hills, residual cones, typically covered by rain forest.
  • Tower karst is the spectacular form with 30-300m high towers with vertical or overhanging sides. The walls are typically bare rock, as the walls are too steep for vegetation.

Tower karst occurs throughout southeast Asia. By far the most extensive and best developed tower karst is in the Guangxi province of southern China. This is the ultimate development of tower karst, in which the residual hills have very steep to overhanging slopes. Other famous areas of tower karst are Vietnam, Thailand and Malaysia. Cone karst occurs in Cuba, Madagaskar and Puerto Rico.

Very common is submerged tower karst on the coast of Thailand and in the Chinese Sea. The towers form steep limestone islands in the sea, sometimes with donlines inside that form salt water lakes with steep walls. This spectacular landscape was used as location for many movies. Most famous examples are (per IMDB):

  • James Bond movies -

    • Man with the Golden Gun - the solar panels coming out of a karst tower -

    • Tomorrow Never Dies -
  • The Beach with Leonardo DiCaprio -

Karst Caves

A cave is an airfilled underground void, large enough to be examined in some way by man. While there are caves in other kinds of rock besides limestone, dolomite and gypsum, they do not have karst features and therefore are not karstic caves


Typical features of karst areas are: 

  • No water on the surface, water oozes away and flows in subterranean rivers.
  • Large springs, often with rapidly changing amout of water, depending on the weather. 
  • Dolines or sinkholes.
  • Karst lakes which have no connection to rivers on the surface. 
  • Dry valleys which were formed when the rivers were still on the surface, before the karst developed. 

Speleothems - Karstic Cave Formations


The term dripstone is applied to a variety of different formations:

Water dripping from the roof of a cavern may form calcium "icicles" or stalactites, or it may build up stalagmites on the floor of the cavern. When stalactites hanging from the roof join up with stalagmites growing upward from the floor and then increase in thickness they form columns known as stalagnates.

Another type of formation which creates a particularly striking effect in illuminated caverns consists of the sinter curtains formed by water trickling from an overhanging rock face. This can produce canopy-like formations. like those to be seen in the Postojna caves.

The shape taken by the dripstone formations depends on a variety of factors, including the calcium content of the water, the amount of evaporation in the cavern and the direction of air movement. They are given their colouring by traces of metallic salts dissolved in the water.

The formations in caves which have been open to the public for a century or more often lack the brilliance of colour found in more recently discovered caves. This is because in the past the caves were frequently illuminated by torches, bundles of burning straw or oil lamps, and soot deposits have dulled the colours.

[insert a story or two about lights]

Not infrequently the roof of an underground cavern will fall in, producing a depression like a bomb crater, known as a doline (sink, swallowhole), which may sometimes reach a diameter of as much as 1100 yd/1000 m. Adjoining dolines occasionally coalesce, forming what is known as an uvala. Stili larger depressions, sometimes covering many square miles and usually surrounded by hills, are known as poljes ("fields") .

Dolines usually provide good agricultural land, since fertile alluvial soil tends to accumulate in them. Poljes with a flat floor, making them particularly suitable for agricultural use, commonly acquire a cover of reddish clay-like soil (terra rossa) deposited by the percolating water.

Examples of Karstic Areas and Caves

The most famous complex of caves is the Postojna Caves (Postoinska Jama) in present-day Slovenia along the subterranean course of the River Pivka, with a number of connected caves, the Otoška Jama, Crna Jama, Magdalenska Jama and Pivka Jama. After pursuing a course which has not yet been traced the Pivka reappears in the Planinska Jama, where it is joined by the River Rak, which has also followed an underground course, passing through the Zadnja Jama and Tkalca Jama (Weaver's Cave). To the east of Postojna is the beautiful Kiržna Jama. (See list of show caves in Slovenia at

The Triestine and Dinarian Karst in Italy and Slovenia are, in fact, only one karst area - a large limestone plateau divided into two parts by the political border. The caves in Slovenija and the caves in Italy are connected. Around Trieste are the Škocjan Caves which belong to the Reka-Rimavo river system. These caves are traversed by the River Reka, with a number of other caves branching off them. Two notable caves in this region are Grotta Gigante and San Giovanni d'Antro. Southwest of Divača are the Divaška Jama and Vilenica Jama (Fairy Cave), still explored, and to the Southeast is the Dimnice Jama (Cave of Mist). 

In Croatian Istrian, the town of Pazin is situated on the rim of a gorge (the foiba of Pazin), into which the little River Pazinski Potok disappears and which is a typical karstic feature. This tremendous hole in the ground, Pazinska Jama, is said to have inspired Dante's vision of the entrance to the Inferno in his Divine Comedy. Both the subterranean caverns and the castle in Pazin, now housing the Ethnographic Museum, are described by Jules Verne in his novel, Mathias Sandorf. A well-known karstic cave of recent discovery is Baredine Jama, near Poreč.

The most famous cave in Lower Carniola is the Taborska Jama (Tabor Cave), with the Ledenica Jama as an antechamber.

An impressive example of karstic landscape can also be seen near Dubrovnik. In the neighbourhood of the little Moslem town of Trebinje is the Popovo Polje, more than 35 miles/60 km long, which fills up with water every September.

*Shown on original text as Yugoslavia.


  • Baedeker's Yugoslavia, translated from the German original, Prentice Hall Press, printed in Great Britain by Jarrold & Sons. Ltd. (Norwich, c. 1987), p. 99-101, 229, 262.
  • A Karst Primer -
  • Show Caves of the World, Karst -
  • Photographs of Sinkholes in Istria - Mirko Gabler.

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This page compliments of Marisa Ciceran

Created: Tuesday, June 18, 2002; Updated: Tuesday, October 16, 2012
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