6.10 Classification of Closed Depressions in Carbonate Karst A Kranjc, ZRC SAZU, Postojna, Slovenia

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6.10.1 Introduction 104 6.10.2 Doline 105 6.10.2.1 Solution Doline 105 6.10.2.1.1 Cockpit 107 6.10.2.2 Collapse Doline 107 6.10.2.3 Caprock Doline 108 6.10.2.4 Subsidence (Suffosion/Dropout) Doline 108 6.10.2.5 Buried Doline 108 6.10.3 Uvala 108 6.10.4 Polje 109 References 110

Glossary by the running water. Water which contains CO2 is more Bogaz (or karst corridor, karst ditch, a corridor or a aggressive and can dissolve more calcium carbonate. Water passage) A street through giant grikes or stone forests and can be enriched by CO2 mostly when percolating through tsingies of the karst in tropical countries. In Turkish soil or decaying organic material. language it means a narrow passage. It entered the karst Diffuse drainage Autogenic recharge, diffuse infiltration, terminology from the karst of Balkans. is the condition whereby precipitation infiltrates into the Cenote Collapsed doline or vertical entrance of a cave, karstic aquifer via many openings in the bedrock thus permanently filled with water, a sort of a window to the allowing approximately uniform amounts of recharge per karst groundwater level. It is a typical feature of shallow unit area of aquifer outcrop. Therefore there are no surface (above the groundwater level) karst, such as on Yucatan streams or surface drainage. Opposite of this is concentrated peninsula. The name has the origin in the language of Maya drainage, point recharge, or allogenic recharge. Indians, that is the 16th century term of Yucatan Maya Holokarst Fully developed karst on pure limestone, dzonot meaning mirror of water, hispanized in cenote. including both surface and underground karst phenomena. Collapse Sudden subsidence of the surface, usually the The term was introduced by J. Cvijic´. Opposite to holokarst breakdown of blocks of the rock (often from the cave is just partly developed merokarst. ceiling) or a part or entire ceiling of the cave. Ponor (swallow hole, sinkhole, sink) Point where Corrosion In karstological terminology it means surface stream sinks into the karst underground. Often the dissolution of carbonate rock. From the rock, water changes ponor means a cave, where an entire stream flows

calcium carbonate, CaCO3, into calcium bicarbonate underground. The term has origin in Serbian language. Ca(HCO3)2, which is soluble in water and transported away

Abstract

Closed depressions are the most characteristic features of karst having dolines among them. Some of the terms, such as doline, uvala, and polje, originate from the Dinaric karst, internationally introduced by J. Cvijic´ in 1893. Karst depressions belong to mezo- and macroforms (from decameter to kilometer scale). The basic feature is the doline, which can be further divided due to its genesis into more main types: solution (the real karst doline), collapse, dropout, buried, caprock, and suffosion doline. The larger depressions, by dimension and form somewhere between a doline and a polje, are the uvala, but genetically they are closer to the doline. Polje (meaning a plain or field in Slavic languages) is the biggest closed depression, its bottom covering several hundreds of square kilometers. Closed depressions, solution dolines and poljes especially, are regarded as indicators of a fully developed karst (holokarst by Cvijic´).

6.10.1 Introduction

Closed depressions are characteristic features of karst. Some Kranjc, A., 2013. Classification of closed depressions in carbonate karst. In: karst regions occur without them, but these are exceptions. Shroder, J. (Editor in Chief), Frumkin, A. (Ed.), Treatise on Geomorphology. Academic Press, San Diego, CA, vol. 6, Karst Taking into consideration the process of karstification and Geomorphology, pp. 104–111. the diffuse drainage directly into the karst underground, their

104 Treatise on Geomorphology, Volume 6 http://dx.doi.org/10.1016/B978-0-12-374739-6.00125-1 Classification of Closed Depressions in Carbonate Karst 105 appearance on the surface is normal. Rainfall on soluble and exceptionally to a few hundreds. The sides can be from gently fissured carbonate rock sinks immediately underground and sloping to vertical, and their form can range from saucer commonly there is no surface runoff. Water corrodes the rock, shaped to funnel shaped or even cylindrical. and initial depressions begin to form. While growing they Enclosed depressions in karst including dolines may be attract more and more water, corrosion is more intensive, and formed by four main mechanisms: dissolution, collapse, suf- depressions become bigger. The difference between the initial fosion, and regional subsidence. Some authors classify dolines depression and the neighbor surface is even greater, the de- according to their shape (Gams, 2004), whereas others by pression deepening is accelerated, and the adjacent surface their origin. Slovene karst terminology includes 14 types of lags behind. dolines. In Panosˇ’s (2001) Karst and Speleology Terminology, In Slovenia, at the time when the notion of karst was not there are 35 types of dolines, according to their evolution yet known to scholars, closed depressions were well noticed by stage, genetic process, type of sediment cover, climatic factor, Valvasor already in 1689. The first researchers, in the modern internal deposits, and shape. But among them are forms that sense of the word, noticed that closed depressions are typical can be classed as other forms, not dolines. Such examples are forms of karst and paid special attention to them. In 1778, B. bogaz, cenotes, and bell-shaped doline, the last is, in fact, a Hacquet described dolines using the German word Kessel shaft. Williams (2004) quoted nomenclature of six main types (¼ kettle), and for polje he used the word Kesseltal (¼ kettle of dolines by seven well-known authors; all agree with two valley). The term already indicates the stress on a closed form types: solution and collapse doline, yet they have different (Kranjc, 2003). In the first half of the nineteenth century, the opinions and names for other types. Largely agreed upon are first modern geological research of karst started in what is six types of dolines (Waltham and Fookes, 2003): solution nowadays Slovenia. The authors mentioned ‘‘funnel shaped doline, collapse doline, dropout doline, buried doline, deepening’’, called dolina by the local people. In 1847, a caprock doline, and suffosion doline (Figure 2). certain Rosthorn reported to Vienna learned society that he has investigated 1000 dolines. In Bosnia and Herzegovina, where poljes are the main karst feature, Austrian geologists 6.10.2.1 Solution Doline started geological research at the end of the nineteenth century and introduced the term polje. J. Cvijic´’s fundamental work The main process involved in the genesis and evolution of a Das Karstpha¨nomen (1893), that is, the ‘phenomenon of solution doline is dissolution or corrosion of the bedrock. The karst’ was probably the decisive work for the introduction of amount of a rock removed in solution depends on the con- the terms doline, uvala, and polje into the international centration of the solute and on the volume of the solvent karstological terminology (Kranjc, 2009). (water draining through the doline). The development of a doline depends on the ability of water to sink into and flow through karst rocks to an outlet spring. On bare limestone (referred to as a bare karst), the recharge is diffuse (autogenic 6.10.2 Doline recharge) and the rainwater directly corrodes the limestone. The corrosion by atmospheric water is most intensive through A doline is perhaps the most characteristic karst feature the upper few meters of the limestone (epikarst or sub- (Cvijic´, 1893), at least among those of exclusively corrosion cutaneous zone) (see Chapter 6.15). Joints, faults, and bed- origin. They are especially common on a mature developed ding planes are discontinuities where the water enters the karst of young folded mountains such as the Dinaric karst rock. In areas with high fissure frequency, there are more and (Figure 1) and similar types of karst. A doline is a natural smaller dolines, whereas particularly large dolines develop in enclosed depression. It is usually circular or subcircular in massive, less fissured rocks (Williams, 2004). The distribution plan and from a few to a thousand meters in diameter. The of dolines depends strongly on the tectonic structure. Align- depth can vary from a few to a few tens of meters, ment of dolines (Figure 3) shows that they evolved along a tectonic line. The density of dolines can vary considerably, also in accordance with their dimensions. The highest density of dolines can reach hundreds and even 1000 per km2, where the whole surface (see Chapter 6.33) is represented by dolines. Therefore, it is not surprising that dolines can reach very high numbers from a regional point of view; on the karst of Cro- atia, for example, 350,000 dolines were digitized (Kranjc, 2009: 170; Matas, 2009). The bottom of a doline is commonly covered by a fine- grained sediment, the nonsoluble detritus of the dissolved limestone, or derived from other fine materials in the sur- roundings, by local washout of soil or loose sediment, or wind deposits. It may be transformed into red karst soil, from terra rossa in humid and warm climates to carbonate brown soil on the karst in more temperate and cooler climates. This is the Figure 1 A rock terrace with dolines above the bottom of Grahovo reason why commonly only the bottoms of dolines can be Polje (Bosnia). Photo A. Kranjc. cultivated on karst. On the plateau of Kras (Slovenia, where 106 Classification of Closed Depressions in Carbonate Karst

Solution doline Collapse doline Dropout doline

Fissure enlargement Surface corrosion Collapsed Fallen Minor collapse Cohesive soil blocks soil

Cave Limestone Cave Limestone Limestone Fissure or cave Cave or fissure

Buried doline Possible Caprock doline Suffosion doline compaction Stoping collapse depression Soil Caprock Soil washing into fissure Noncohesive soil

Limestone Cave

Limestone Caves and fissures Limestone Cave Fissure or cave

Figure 2 Six main types of dolines. Reproduced from Waltham, A.C., Fookes, P.G., 2003. Engineering classification of karst ground conditions. Quarterly Journal of Engineering Geology and Hydrogeology 36, 101–118.

Figure 4 An example of a man-made doline (under Dinara Mt., Figure 3 A line of solution dolines in Dinaric karst (Southern Velebit Bosnia) – man gathered loose rocks and buried them in the bottom Mt., Croatia). Photo A. Kranjc. of doline, scraped soil from the slopes, and spread it over to get more surface for cultivation. Photo A. Kranjc. the term ‘karst’ came from), people buried the stones derived by cleaning the slopes of dolines into their bottoms, scraped the soil from the slopes and from the neighboring surfaces, middle of the nineteenth century when geologists started and spread it over the bottom. In this way, the flat bottom of modern research on karst in Kranjska (Carniola, Slovenia), the doline becomes larger and becomes thicker soil. In the one of the Austrian hereditary countries, they soon perceived local language, such a doline is called ‘man-made doline’ that dolines are a special form of limestone landscape. This (Figure 4) (Gams, 2004). Due to the fact that dolines are funnel-shaped (Trichterfo¨rmige in German) depressions they closed, they may have a specific micro-climate with tempera- called a funnel (Trichter), but often they simply used the local ture inversion. In some cases of very big and deep dolines, this term, doline. Gradually, the word doline (plural form of do- inversion is expressed in a vegetation inversion too (Ba´ra´ny- lina) became the term for collapsed dolines (steep or pre- Kevei, 1998). cipitous) and for the normal (corrosive, solution) dolines they The inhabitants of the Kras plateau call a doline, dolina took the term Trichter (a funnel). In Cvijic´’s highly influential and variants such as dol and dolec. In Slovene, as in many work Das Karstpha¨nomen (1893), there is a separate chapter other Slavic languages, a dolina simply means a valley. In the titled ‘Dolinen’, where he treats not only dolines but also all Classification of Closed Depressions in Carbonate Karst 107 sorts of closed depressions including some karst springs, with general, the cockpit doline is greater than normal solution the exception of uvalas and poljes. He decided to use the term doline (in temperate karst) with secondary fluvial relief doline ‘‘after the name of small hollows in the part of Car- (small ravines of streams after heavy rains, draining into niola, between Ljubljana and Planina especially.’’ In inter- ponors in the bottom). Thus, a great number of these national use, doline means primarily solution doline, while dolines – cockpits – are by some properties closer to an uvala the other main type is called collapsed doline. than to a solution doline. The term sinkhole entered into international use from America. Basically, it means sinkhole, swallow hole, and ponor (see Chapter 6.11), where the water sinks underground. 6.10.2.2 Collapse Doline Sometimes, the term is used to refer both to dolines and to depressions with ponor. In America, it means a special type of A collapse doline is formed mainly by collapse, that is, rapid collapse doline, similar to suffosion or dropout doline, where downward movement of the ground. The role of solution is the sudden collapse can cause a great damage. Thus, the terms indirect – by enlarging the cave under the surface, to lower the sinkhole and doline are not strictly synonymous (Williams, surface, to enlarge the fissures to a point where the ceiling is 2004). too weak and breaks – collapses, and a collapse doline is One of the first books on karst in Slovene language, formed (Williams, 2004). It is preferentially subcircular in Geography from 1874, does not use the term doline but in- plan, commonly between a few tens to a few hundred meters stead, the term sinkhole. To avoid confusion with the fluvial in diameter, with very steep to vertical or subvertical slopes. Its valley, Slovene geographers very early (1908, 1913) used the width is bigger than its depth; otherwise, it is termed a karst term vrtacˇa, which was later proposed by Cvijic´ to be used in shaft. Over time, the sides of a collapse doline degrade mostly the Serbian language. After World War II, Slovene karstologists by weathering. The slopes become less and less steep, and stopped using the term doline completely. The same hap- debris infills the bottom, which flattens. By this time, a col- pened in other Slavic languages; they do not use the term lapse doline loses its typical form and becomes similar to a dolina, but an appropriate expression in their language big, bowl-shaped solution doline. (Kranjc, 2009). The biggest collapse dolines have a volume of tens of millions of cubic meters. One of the reasons of the collapse is 6.10.2.1.1 Cockpit thinning of the cave ceiling of large caves. The process of Cockpit karst is a karst terrain in a warm and humid belt the thinning is not only corrosion and subaerial denudation, dotted with big solution dolines – cockpits, as they are called but also breaking down of the rocks from the cave ceiling. in Jamaica. The rims of these big dolines touch; the available Big cave chambers (commonly referred to as a breakdown space is occupied by depressions (Figure 5). The solutions chamber) with relatively thin ceiling may be situated at the dolines – cockpits – are approximately star-shaped in form edge of karst plateaus, in the hinterland of karst springs or and are separated by irregular ridges and hills in the shape of ponors, and these are places where collapse dolines are com- cones, so a synonym of cockpit karst is cone karst. Topo- monly situated. A good example is Sˇkocjanske Jame (Slovenia) graphic divides of the dolines have a polygonal pattern and listed in the UNESCO World Natural Heritage (United such karst is also called polygonal karst (Williams, 2004). Nations Educational, Scientific and Cultural Organization, Commonly, a cockpit is a synonym for tropical doline. In UNESCO). If the bottom of a collapse doline reaches the karst groundwater table (or the level of the water table changes) the bottom of such collapse dolines can be periodically or per- manently flooded. In such a case, the problem can be how to distinguish without detailed studies a collapse doline from a cenote or a blue hole, if a collapse doline is submerged by the sea. A closed depression which is deeper than larger is defined as a speleological object. Therefore, depending on their depth/ width ratio, some cenotes can be classified as speleological objects while others are surface features – dolines. In the professional literature, cenotes belong either to the surface forms – dolines (Panosˇ, 2001), or to subterranean forms – caves (Gunn, 2004). An illustrative example is Crveno Jezero (Figure 6), a collapse doline, or vertical cave, in Dalmatia (Dinaric karst). The diameter is about 300 m, the depth is 528 m with the bottom 6 m under the sea level. The lower part of the doline (about 280 m deep) is filled by water – the lake (Garasˇic´, 2000). Due to their large size and form, collapse dolines are outstanding surface features and therefore easily noted in the field. This is why people commonly refer to them with special Figure 5 Large cockpit in tropical karst (Leye Co., Guangxi local terms. In Slovenia, there are nearly 10 local expressions province, China). Photo A. Kranjc. for collapse dolines and commonly each collapse doline has a 108 Classification of Closed Depressions in Carbonate Karst

Figure 7 Xiaozhai Tiankeng (Chongqing Municipality, South China), 662 m deep collapse doline with a volume of 119.3 million m3. Photo A. Kranjc.

visible part of the doline, is in noncarbonate rock and also the debris at the bottom is of the same rock.

6.10.2.4 Subsidence (Suffosion/Dropout) Doline A subsidence doline is a closed surface depression in the form of a solution doline, but in a sediment cover of carbonate rock. It is developed by evacuation (suffosion) of sediment cover downward into a karst void underneath. The result is rapid or gradual subsidence of the surface. According to the type of subsidence, the subsidence dolines are divided into two types: the dropout and the suffosion dolines. In cohesive sediment, Figure 6 Crveno Jezero (Red Lake) collapse doline above the the subsidence is often sudden and the result can be cata- Imotsko Polje (Croatia), more than 500 m deep and half under water. Photo A. Kranjc. strophic. This type of a doline is called a dropout doline. In noncohesive sediment, most commonly soil, the clayey fraction tends to move as slurry into the cavity underneath, whereas the coarser fraction remains nearer to the surface. Such a type of special name too. The biggest known collapse doline on the doline is called a suffosion doline (Figure 8) and it is usually of Kras plateau has a volume of 11 million m3 (Kranjc, 2005). relatively small dimensions, in the meter scale (Williams, 2004). Whereas, on the high karst plateaus of southeastern Asia, well surveyed especially in China, extremely large and deep collapse dolines developed. They are over 500 m deep and 6.10.2.5 Buried Doline 3 their volume exceeds 100 million m . Locally they are called This is a normal solution doline filled with sediment. On the tiankeng (tian ¼ sky, nature, keng ¼ hole). Among the kar- surface, there is no evidence that in the bedrock there is a stologists there is a tendency to include tiankeng in the closed depression – buried solution doline. They can be lo- international karst terminology. The biggest known is Xiao- cated by earth excavation or by geophysical or geotechnical zhai Tiankeng (Figure 7) (Xinlong karst in South China), 662 survey. Sediment in such dolines can be of economic value, 3 m deep with a volume of 119.3 million m (Zhu and Chen, such as bauxites (Williams, 2004). Good examples are big 2005). In most cases, an underground river is flowing at the buried dolines of the Ravni Kotari (¼ flat region) corrosion bottom of a tiankeng. plain along the Dinaric coast of the Adriatic Sea. They are filled by bauxite and covered by large conglomerate covers of Tertiary (Jelar) formation. 6.10.2.3 Caprock Doline It can be said that a caprock doline is a subtype of a collapse doline. The general process is the same as with a collapse 6.10.3 Uvala doline. A void in limestone grows, its ceiling becomes too thin or too weak, and it collapses. But in the case of a caprock According to the Slovene karst terminology (Gams, 1973), an doline, the carbonate rock is covered by a layer of non- uvala is a closed depression of a bowl shape on a karst surface, carbonate rock – caprock. The upper part, often the only usually smaller than a polje and greater than a doline with Classification of Closed Depressions in Carbonate Karst 109

Figure 8 Suffosion type of subsidence doline on the Ice Mt. above Figure 9 Losˇki Potok, an uvala large enough for a village and fields the town of Kungur (Permski krai, Russia) in the Pre-Ural evaporite (Dinaric karst, Slovenia). Photo A. Kranjc. karst. Photo A. Kranjc. study of the uvala question shows that it would not be wise to irregular bottom due to incorporated dolines. Regarding its abandon the term, because there are distinct closed de- form, it is also between the polje and a doline. The term was pressions that are neither dolines nor poljes and have quite introduced from the Serbian language (it means a valley, a gap clear common characteristics. between two mountains) by Cvijic´ in 1901. His definition is as follows: ‘‘Uvala is a karst depression, bigger than doline, few 100 m long, sometimes even 2-3 km. As a rule there are do- 6.10.4 Polje lines in its bottom. The brinks of those dolines are lower than the brink of the uvala’’ (Cvijic´, 1926). The rim of an uvala is Polje (see Chapter 6.11) is the largest flat-floored closed karst irregular in general; the bottom is bare or covered by soil or depression, typical especially for some types of well-developed sediment. Uvala is an international term despite the tendency karst in young folded mountain systems, such as the Dinaric to abandon it. According to Cvijic´, an uvala is formed by so- karst, karst in Epirus, Peloponnesus, Taurus, Zagros, etc., or in lution through the coalescence of dolines into a bigger de- karst that is called by Cvijic´ holokarst or fully developed pression. Further evolution leads to a polje by the coalescence mature karst. The surface of the polje’s bottom can range from of uvalas. Some authors do not agree that uvalas are formed a few km2 to 4500 km2. It is suggested that the short axis of a exclusively by the corrosion of limestone and it is mostly polje bottom should not be shorter than 400 m (Gams, agreed that they are not formed by the coalescence of dolines. 1978). The biggest polje of the Dinaric karst, Licˇko Polje, Although an uvala is not an entry in Gunn’s (2004) encyclo- covers nearly 500 km2 (Ford and Williams, 1989). A polje pedia, the author of a chapter on dolines, P. Williams, men- commonly has a noninterrupted rim. It can also be in- tions it. He even states that ‘‘Individual dolines may merge to completely closed, with its rim open due to different reasons, form compound closed depressions (known as uvalas)y’’. such as a surface river flowing out; such a polje is called an A similar nonagreement regards the further evolution towards open polje. A polje has to have a relatively large and flat a polje by the coalescence of uvalas. Panosˇ (2001) stressed that bottom (Figure 10). The reason for levelness may be the uvalas are features of covered karst. According to his defin- sediment cover over relatively rough bedrock. The drainage ition, the bottom of an uvala can be flooded sometimes or from the polje is a part of the regional karst hydrology. From a even contain a permanent lake. Considering the prevailing regional point of view, the location of a polje is strongly process, uvalas can be classified among dolines. Because the connected to the tectonic structure. In the Slovenian Dinaric genesis is not clear and the researchers do not agree upon this karst, for example, five poljes are located along the regional question, it has been proposed not to use this term any more (160 km long) fault line. The great majority of poljes in the (Lowe and Waltham, 1995; Palmer, 2007). Some authors use Dinaric karst has a Dinaric orientation, meaning that their the term strictly in a morphological sense: if it is neither a long axis is oriented from NW to SE. This is the direction of doline nor a polje, it has to be an uvala. In some cases, it is general tectonic structures, which is also the direction of major difficult to distinguish between a big atypical doline or an morphological units. Poljes are polygenetic; they are the uvala, as well as between uvalas and atypical small poljes. combination of different processes. Tectonically, predis- Uvala can be either very deep, on high karst plateaus espe- position is of primordial importance, not only for the lo- cially, with temperature and vegetation inversion, or having a cation, but also for their main properties. In principle, polje is low rim difficult to perceive. Uvalas are typical features of a karst phenomenon on carbonate terrain; however, due to the Dinaric types of karst (Figure 9). In tropical karst, the large dimensions, other rocks may be included, either as a part equivalent of uvala is a glade. The term comes from Jamaica of polje’s margin or as a part of its bottom. If the formation of and means closed depression like an uvala with wet grassland the main depression is initially the work of tectonic forces or or marsh at the bottom (Sweeting, 1972). The last detailed water, either through erosion or through corrosion, still 110 Classification of Closed Depressions in Carbonate Karst

flooded, but otherwise it is dry. By the dimensions, turloughs may range from doline to polje, but their hydrological char- acteristics justify calling them by a special name. Recent re- search shows that such features are not restricted to the karst of Ireland but occur elsewhere too (Skeffington and Scott, 2008). The international term polje originated in the karst of Bosnia and Herzegovina, where they are the main karst fea- ture. Austrian geologists started to study Bosnian and Herze- govinian karst, a part of Dinaric karst, in the second half of the nineteenth century and introduced in their published works the term polje. Finally, the term became international through the works of J. Cvijic´. In Bosnian as well as in other languages of Southern Slavs, the word polje means plain, often culti- vated, and even field. In Slavic languages, the original meaning Figure 10 Cerknisˇko Polje (Dinaric karst, Slovenia) – one of the best examples and the earliest-studied polje. Photo A. Kranjc. of the word is something large, wide, and broad. Local people called a polje the large flat surface of the polje bottom, which can be cultivated, in contrast with polje’s slopes and sur- rounding dry, bare, limestone landscape. In most of the Slavic karst terminologies, the adjective karst is added to the term polje: karst polje, not to be confused with another meaning of the word.

References

Ba´ra´ny-Kevei, I., 1998. Geological system of karsts. Acta Carsologica 27(1), 13–25. Cvijic´, J., 1893. Das Karstpha¨nomen. Versuch einer morphologischen Monographie. Geographische Abhandlungen (Penck), (B), 5/3. Wien, E. Ho¨lzel, Stuttgart, 114 pp. Cvijic´, J., 1926. Geomorfologija, 2. Srpska akademija nauka i umetnosti, Beograd. Ford, D., Williams, P., 1989. Karst Hydrogeology and Geomorphology. Chapman and Hall, London, 601 pp. Gams, I., 1973. Slovenska Krasˇka Terminologija. Katedra za fizicˇno geografijo FF, Ljubljana, 75 pp. Figure 11 Turlough – dry lake in the karst of Ireland (Castlerea, Gams, I., 1978. The polje: the problem of definition. Zeitscbrift fu¨r Geomorphologie N.F. 22(2), 170–181. Roscommon Co.). Photo A. Kranjc. Gams, I., 2004. Kras v Sloveniji v Prostoru in Cˇasu. Zalozˇba ZRC, Ljubljana, 515 pp. remains a matter of discussion. They can even differ from one Garasˇic´, M., 2000. Speleohydrogeological Research of Crveno jezero (Red Lake) example to another. near Imotski in Dinaric Karst Area (Croatia). Proceedings of the second Croatian Very few poljes correspond to all criteria of the polje def- Geological Congress. Cavtat-Dubrovnik, Croatia, pp. 587–590. Gunn, J. (Ed.), 2004. Encyclopedia of Caves and Karst Science. Fitzroy Dearborn, inition. Because of their complex origin and evolution, there New York, NY and London, VII–XVIII, 902 pp. are many classifications of poljes according to different cri- Kranjc, A., 2003. Balthasar Hacquet, predecessor of modern karstology. Hacquetia teria, such as geological, morphological, and hydrological 2/2, 129–138. characteristics. The most complex overview of types of poljes is Kranjc, A., 2005. Some large dolines in the Dinaric karst. Cave and Karst Science 32(2&3), 99–100. ˇ given in Panos’s (2001) terminology, where, according to Kranjc, A., 2009. An example of karst terminology evolution: from ‘‘Dolina’’ to different authors, 46 types of poljes are classified by geologi- ‘‘Tiankeng’’. Carsologica Sinica 28(2), 169–174. cal–structural position, origin, position on carbonate/non- Lowe, D.J., Waltham, T., 1995. A Dictionary of Karst and Caves. Cave Studies carbonate rocks, macro-relief, hydrogeology, climate, ground Series 8. BCRA, London, 40 pp. plan, and cross section. Gams’ (2004) classification consists of Matas, M., 2009. Krsˇ Hrvatske, Geografski pregled i znacˇenje. Geografsko drusˇtvo, Split, 264 pp. five types based on lithological, morphological, and hydro- Palmer, A., 2007. Cave Geology. Cave Books, St. Louis, MO, 454 pp. geological conditions: border, peripheral, kettle form, pied- Panosˇ, V., 2001. Karsologicka´ a speleologicka´ terminologie. Knizˇne´ centrum, Zˇilina, mont polje, and polje in the karst water table level. On the 352 pp. other hand, Ford and Williams (1989) proposed three main Skeffington, M.S., Scott, N.E., 2008. Do turloughs occur in Slovenia? Acta Carsologica 37(2–3), 291–306. types only: border, structural, and base-level polje. Sweeting, M.M., 1972. Karst Landforms. Basingstoke, London, 362 pp. Closed depressions called turlough (Figure 11), known Waltham, A.C., Fookes, P.G., 2003. Engineering classification of karst ground from Ireland, may be included under the term polje. The word conditions. Quarterly Journal of Engineering Geology and Hydrogeology 36, turlough means dry lake in the Irish language. Turloughs are 101–118. closed depressions generally but not necessarily smaller than Williams, P., 2004. Dolines. In: Gunn J. (Ed.), 2004. Encyclopedia of Caves and Karst Science. Fitzroy Dearborn, New York, NY, and London, pp. 304–310. polje with flat bottoms and relatively low, not always well Zhu, X., Chen, W., 2005. Tiankengs in the karst of China. Cave and Karst Science noticeable, margins. During the rain period, the bottom is 32(2&3), 55–66. Classification of Closed Depressions in Carbonate Karst 111

Biographical Sketch

Born 1943 in Ljubljana (Slovenia), Andrej Kranjc studied geography and archaeology; in 1972, he did an ad- vanced study course of speleology in France; in 1977, he completed his master’s degree; and, in 1986, he received his doctor’s degree at Ljubljana University. He is a retired scientific adviser at the Karst Research Institute (Postojna), Scientific Research Centre of the Slovenian Academy of Sciences and Arts, Professor Emeritus and Head of the doctoral programme Karstology at the University of Nova Gorica, and a member of the Slovenian Academy of Sciences and Arts. He is a member of different boards of professional institutions and of editorial boards. As an expert, he visited karst all over the world. Among other awards, he is also a French Chevalier dans l’Ordre des Palmes Acade´miques.