> Glossary of karst landforms <
28 terms, from dolines to cave formations, in Italian, English, Slovenian and German.
Tap a point in the drawing: the karst landform opens below.
Dolines or sinkholes
Dolines are forms typical of karst regions. They are configured as roughly circular or oval-shaped depressions, varying in size from a few meters to several hundreds of metres in diameter. If a cavity is found below the sinkhole and its ceiling collapses, a collapse doline is formed such as, for example, the Grotta Noè cave in the Karst near Trieste.
Polje
Poljes are large enclosed depressions of mixed origin. They are in fact linked to karst phenomena (the dissolution of calcium carbonate) and are often located in tectonic depressions or in contact between soluble rocks (for example limestones) and insoluble ones such as flysch.
They have dimensions that reach several tens of kilometres in length, the sides are steep and sloping, while the floor is flat, rocky or clayey.
In active poljes there is periodic flooding of the plain when the dolines fail to drain the water or when they act as outlet points for groundwater.
Uvala
Uvalas derive from the enlargement or fusion of two or more dolines. Their contours are sinuous and lobed with a maximum depth of a few tens of metres. The alignment of several sinkholes usually indicates the presence of geological structures such as faults or fold axes,
Blind valleys
Blind valleys are river valleys along the course of which, usually in the final stretch, one or more sinkholes have opened up. Upstream of these the incision continues to deepen, but downstream there is no further running water and therefore its development is interrupted, forming a dry valley, while the area around the sinkhole (into which the water is absorbed) evolves as a doline and the upstream part as a river valley.
In the Classic Karst there is the the blind valley of the upper course of the River Reka (Timavo), which flows for over fifty kilometres over impermeable ground, meeting the limestone near the village of Vreme in Slovenia where it is swallowed up underground near the Škocjan caves (Škocjanske Jame).
Karren
Karren are the small shapes that are sculpted on the surface of soluble rocks directly exposed to atmospheric agents or covered by soils.
They are linked either to the active dissolution of water flowing on the more or less steep sides or to static dissolution brought about by standing water in the depressions.
Overall, the dimensions of the shapes vary from a few millimetrers to tens of metres, but the extension of the sculpted outcrops may also reach many square kilometres.
Crevasses
Karst crevasses are deep fractures, linked to the preferential outflow paths of the water, guided by rock fracturing. The sides are always steeply sloped, the bottom is flat or an open "V". From a genetic point of view they are similar to karren. However, while in karren it is the maximum slope that guides the flow of water, in crevasses it is the planes of discontinuity (usually rock fractures) that condition the direction of movement.
Griže
Griže are screes made up of small blocks of limestone with sharp edges.
They are formed following the fragmentation of the rocky substrate due to the progress of Karst processes along surfaces of discontinuity.
Rillenkarren
The are minute forms represented by straight furrows (about 1 cm deep, 1-4 cm wide and 5-50 cm long) with a rounded cross-section. They are generally grouped together in groups that may resemble a comb, a pen, a bundle or in little islands and are separated by a sharp "ridge" which acts as a watershed and are typical of slightly inclined surfaces. They originate from the dissolution of the rock due to the flow of rainwater along its surface and along the lines of maximum slope. Downstream of the grooves there are often smooth surfaces which correspond to the areas where the water is capable of forming a continuous layer by joining the various streams of water which then flows in a homogeneous fashion.
Rinnenkarren / Karst flutes
Karst furrows are more than 5 cm wide, more than 3 cm deep, and at least 100 cm long and follow the maximum slope of the limestone surface. They have various shapes, the section is always U-shaped, but the sides can be variable in steepness. The development is straight as well as tortuous or meandering, the bottom is smooth, often hollowed out by a secondary groove. The longitudinal profile is sometimes characterised by a stepped pattern due to the presence of small hollows.
Dissolution terraces
Solution terraces are extensive smooth surfaces are located downstream of a set of grooves where the surface water forms a continuous layer with a homogeneous flow.
Dissolution holes
Dissolution holes are tubular karst microforms with a circular or elliptical section, with a diameter ranging from millimetric to decimetric, like holes drilled in the rock which form in correspondence with tiny channels in the fractures.
The section of the cone of the hole appears wider, proceeding from the bottom upwards and this is due first to capillarity phenomena and then to humid air circulation.
Kamenitza
Corrosion pans (known internationally using the Slovenian term Kamenitza) are karst micro-depressions created by the presence of organic matter. The trays have depths from 2 to 50 cm with diameters from 4 to 400 cm. The bottom is almost always horizontal, the section is flat or bowl widened towards the bottom.
Pans widen faster than they deepen as corrosion is more active at the edges than at the bottom.
Hums
Hums are what remains of a limestone relief. These karst structures are defined as towers or hum, a term of Serbo-Croatian origin which indicates precisely the residual limestone reliefs. The intense and continuous activity of dissolution by meteoric water on the surrounding rocks and the simultaneous presence of a dense network of fractures present in the calcareous rock mass, over time can cause a slow but progressive widening of the flowways, reaching the point where it divides the original calcareous outcrops into blocks, sometimes of large dimensions. When they are numerous and juxtaposed they are called “cities of rock”.
roofless caves
The roofless caves are ancient cavities without a vault because they have been "uncovered" by the erosion of the topographic surface. They are often filled with clayey sediments, concretions or collapses even if it frequently happens that rainwater washes away the sediments contained in them and this justifies the fact that most of the roofless caves appear on the surface as depressions rather similar to sinkholes.
Caves
Caves are natural cavities, one of the most important karst environments of the Karst above Trieste and over 3300 have been discovered in this area alone.
These caves originated following tectonic thrusts of a geological nature that have affected the area for over 30 million years. The cracks formed in the limestone rock have been widened by erosion and the slow process of dissolution by rainwater made more acidic by the presence of carbon dioxide. The entire calcareous subsoil of the Karst is a succession of distinct cavities with various names depending on their shape and size, including galleries, tunnels, meanders, wells, abysses, caves, halls and caverns. Inside the cave, the redeposition of the calcium carbonate builds spectacular forms of calcite concretions which take the name of stalactites, stalagmites, eccentrics, columns, gours, flowstones and pisolites.
To find out where the caves are located in the Classical Karst and to get further information, we advise you to consult the maps on display in the entrance hall.
Stalactites
Stalactites and stalagmites are the most common and well known concretions or speleothems.
The stalactites are formed from the ceiling. The falling drop of water loses carbon dioxide by diffusion in the atmosphere of the cavity and deposits around it crystals of calcite the growth axes of which are perpendicular to the surface from which the stalactites drip (or on which the waters flow).
Water percolates through a central tube called a soda straw, which contributes to its vertical growth.
If the soda straw fails to drain the drops, the water also percolates through the external surface and the stalactite also grows radially.
Stalagmites
Stalactites and stalagmites are the most common and well known concretions or speleothems.
Stalagmites are formed where a drop of water falls on the floor and which, upon impact, disperses carbon dioxide into the atmosphere of the cavity and deposits calcite crystals.
The extremely variable size and shape of the stalagmite depend not only on the speed of fall (and therefore on the height of the drop), on the quantity of water and on its regime (which is also influenced by the external climate). The classic cylindrical shape with the ogival apex originates as the deposition is maximal at the point of impact and tends to decrease radially.
Complex stalagmites are frequent, consisting of an intense and continuous drip, with shelves and secondary stalactites that complicate the structure by enlarging and moving it.
Tubulars, soda straws, cannulas
Tubulars are particular stalactites the diameter of which remains constant and coincides with that of the drop that passes along it (0.4 - 6 cm).
The dripping must be slow to allow the deposition of the circular crown material but also fast enough not to allow concretion to occur in the internal section.
Thus a tubular cannula is generated, whose millimeteric walls are made up of calcite crystals with an axis of growth in the direction of the force of gravity.
If the water flows along the external wall, crystals are generated with an axis perpendicular to the cannula and therefore a stalactite begins to form.
Columns
They are concretions that are formed by the union of a stalactite and a stalagmite which, growing together, are welded into a single body thus generating the column.
Curtains
Curtains are formed when, before detaching from the ceiling, the drop of water runs along the wall for a certain distance depositing the calcium carbonate, and giving rise to a veil-like structure.
The different bands of a sail vary in thickness and color according to the extent of the percolation and the percentage of impurities due to metal oxides, processes which depend on the external climate.
Canopies
These are concretions protruding from the walls which are characterised by a flat or inclined lower surface on which subsequent further phases of concretions occur. The formation of the lower surface is linked to various mechanisms including the rapid variation over time of the water flow, the presence of a sediment which is then washed away, or the presence of a water surface whose level remains stable over time
Discs
The concretions formed by two circular and flat elements and separated from each other by a feeding plane in which the water flows are called discs.
Gours
Gours are actual calcite dams that form when the laminar flow of water flowing over a floor slows down and concretion processes are triggered on the face of the structure.
The dam can grow in height and width and act as a barrier to water.
Cave pearls
Pisolites, or cave pearls, are spherical concretions or that originate in basins with moving water. They form by accretion around a solid nucleus, such as a grain of sand or a fragment of rock. They can be found in waters significantly supersaturated with calcium carbonate. The greater the saturation, the more the formation of new growth centers are favoured with respect to the growth of existing ones and therefore there will be smaller, more numerous pisolites.
Moonmilk
Moonmilk is an agglomeration of microcrystalline substances which, impregnated with water, is soft and plastic. When dry it reduces to a powdery appearance. It is formed mainly by the precipitation of calcium carbonate from supersaturated waters, in conditions such that the seeds of crystallisation remain disordered without developing clear crystals.
Eccentrics
Eccentrics are concretions that have the main characteristic of developing in all directions and they can vary from a few millimeters to several metres in length, while the diameter ranges from fractions of a millimeter to over 10 centimetres.
Characteristics common to all eccentrics are that the channel that develops inside the eccentric for the deposition of calcium carbonate takes a completely independent shape and has a very small diameter of between 0.008 and 0.5 mm. Their curvature can be constant and continuous or vary according to angles defined by the crystalline lattice.
Flowstones
Flowstones are layers of limestone deposited along the walls by layers of water. They are also not limited by gravity and can grow to considerable sizes.
Coralloids
Coralloids are concretions formed by more or less spherical globular microforms varying in diameter, from a few millimetres to a couple of centimetres.
Coralloids are formed when water rises up the surface of the rock by capillarity and, following evaporation, deposits particles (microcrystals) of calcite on its surface. Thus a globular structure is formed since the coralloid can develop in all directions and, once it reaches a certain size, second order coralloids can begin to develop upon it.
Karst glossary produced for the Centro Didattico Naturalistico di Basovizza (Autonomous Region of Friuli Venezia Giulia), texts validated in Italian, English, Slovenian and German.