6.10 Classification of Closed Depressions in Carbonate Karst A Kranjc, ZRC SAZU, Postojna, Slovenia r 2013 Elsevier Inc. All rights reserved. 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 kmÀ2, 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.