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Unroofed caves are an important feature of karst surfaces: Examples from the classical karst
Abstract
Unroofed caves are old caves that due to the lowering and dissection of the karst surface have been uncovered or split. Karstologists often explained various depressions in the karst surface as dolines or merely the consequence of lithological rock characteristics and their fracturing. During the construction of over a 50-kilometre long expressway, 300 caves were discovered, of which 80 are unroofed. Unroofed caves are becoming an ever more distinctly readable phenomenon on the surface. They reflect the development of the aquifer with its geological, geomorphological, hydrological and climatic characteristics.
... They present the former underground features that are now exposed on the surface [1,2]. Unroofed caves as karst phenomena have been thoroughly studied mostly in Slovenia [1][2][3][4][5][6][7]. However, some international studies also describe these phenomena but mainly without speleological or geomorphological interpretations [8][9][10][11]. ...
... An additional sign for identifying unroofed caves are the geomorphological features of the surrounding terrain. Depending on the cave type and the manner in which denudation cut the cave, unroofed caves can appear as elongated dolines, series of dolines, shafts or linear to irregular depressions completely filled with sediments [2,6,7]. Apart from that, surface processes can strongly reshape and modify the segments of the former cave, so they are sometimes completely masked, meaning that their speleogenetic origin cannot be demonstrated. ...
... The relatively complex terrain of the study area, full of dolines, complicates the task of recognizing the various features as a cohesive whole model, compared to unroofed cave systems observed in Classical Karst, where segments of unroofed cave systems are easier to identify (e.g., [1,2,5,7]). To study the location, size and shape of unroofed caves, high-resolution LiDAR data proved to be very useful [2]. ...
Ground penetrating radar (GPR) using a special unshielded 50 MHz Rough Terrain Antenna (RTA) in combination with a shielded 250 MHz antenna was used to study the capability of this geophysical method for detecting cave sediments. Allochthonous cave sediments found in the study area of Lanski vrh (W Slovenia) are now exposed on the karst surface in the so-called "unroofed caves" due to a general lowering of the surface (denudation of carbonate rocks) and can provide valuable evidence of the karst development. In the first phase, GPR profiles were measured at three test locations, where cave sediments are clearly evident on the surface and appear with flowstone. It turned out that cave sediments are clearly visible on GPR radargrams as areas of strong signal attenuation. Based on this finding, GPR profiling was used in several other places where direct indicators of unroofed caves or other indicators for speleogenesis are not present due to strong surface reshaping. The influence of various field conditions, especially water content, on GPR measurements was also analysed by comparing radargrams measured in various field conditions. Further mineralogical-geochemical analyses were conducted to better understand the factors that influence the attenuation in the area of cave sediments. Samples of cave sediments and soils on carbonate rocks (rendzina) were taken for X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses to compare the mineral and geochemical compositions of both sediments. Results show that cave sediments contain higher amounts of clay minerals and iron/aluminium oxides/hydroxides which, in addition to the thickness of cave sediments, can play an important role in the depth of penetration. Differences in the mineral composition also lead to water retention in cave sediments even through dry periods which additionally contribute to increased attenuation with respect to surrounding soils. The GPR method has proven to be reliable for locating areas of cave sediments at the surface and to determine their spatial extent, which is very important in delineating the geometry of unroofed cave systems. GPR thus proved to be a very valuable method in supporting geological and geomorphological mapping for a more comprehensive recognition of unroofed cave systems. These are important for understanding karstification and speleogenetic processes that influenced the formation of former underground caves and can help us reconstruct the direction of former underground water flows.
... 3. Manifestation of unroofed caves on the karst surface and a simple conceptual model of the study area Unroofed caves are caves or cave segments filled with sediment that appear on the karst surface as karst denudation removes the rock above them. The shape and visibility of unroofed caves on karst surfaces depends on the cave type and the manner in which the denudation cuts the cave (Fig. 5) (Šušteršič, 1998;Mihevc, 2001;Knez and Slabe, 2002). ...
... In the late Pleistocene, such depressions were subject to intensive weathering and slope processes that resulted in typical Dinaric doline geometry (Šušteršič, 2006): rounding of the upper rim and equilibration of the slopes. The well-developed basic attributes that also characterize a solution doline show that individual segments of unroofed caves are able to develop these superficial features, as Mihevc et al. (1998) and Knez and Slabe (2002) have previously established. We presume that denuded cave segments evolve into dolines at locations where the cave passage widens considerably forming a hall, and where the effective sediment transition into karst underground is established. ...
... Some examples of surface manifestations of unroofed caves: the denudation cuts the passage: a) parallel, b) transversally, or c) at loops. Reproduced with permission fromKnez and Slabe (2002). ...
The bare karst surface in the southeastern part of Krk Island (Croatia) is characterized by different surface karst features, such as valley-like shallow linear depressions and partially or fully sediment-filled depressions of various shapes and sizes. They were noticed due to locally increased thickness of sediment and enhanced vegetation but had not yet been systematically studied and defined. Considering only the geometry of the investigated surface features and the rare traces of cave environments detected by field surveys, it was unclear which processes (surface karstification and/or speleogenesis) contributed most to their formation. The low-frequency ground penetrating radar (GPR) method using a special 50. MHz RTA antenna was applied to study and describe these karst features. Three study sites were chosen and 5. km of GPR profiles were positioned to include various surface features. The results obtained from the GPR investigation lead to the following conclusions: (1) an increased thickness of sediment was detected in all the investigated depressions indicating their considerable depth; (2) areas between different depressions expressed as attenuated zones in GPR images reveal their interconnection; (3) transitions between surface and underground features are characterized by a collapsed passage visible in the GPR data; and (4) an underground continuation of surface valley-like depressions was detected, proving the speleogenetic origin of such features. Subsurface information obtained using GPR indicates that the valley-like depressions, irregular depressions completely or partially filled with sediment, and some dolines are associated with a nearly 4. km-long unroofed cave and developed as a result of karst denudation. In the regional context, these results suggest long-lasting karstification processes in the area, in contrast to the pre-karstic fluvial phase previously assumed to have occurred here. This research is the first application of the GPR method to survey unroofed caves worldwide and the first detailed study of such karst features in Croatia. The low-frequency GPR proved to be an efficient method not only for detecting underground continuations but also for distinguishing and identifying surface features and transition zones between surface and subsurface segments of unroofed caves and can therefore be used for recognizing similar geomorphological features.
... Karstologists and road builders (DARS d.d.) cooperate successfully in the planning and building of motorways in Slovenia (Knez et al. 2004, Knez & Slabe 2001, 2002Šebela et al. 1999). ...
... Povzetek Krasoslovci z graditelji (DARS d.d.) uspešno sodelujemo pri načrtovanju in gradnji avtocest v Sloveniji (Knez et al. 2004, Knez & Slabe 2001, 2002, Šebela et al. 1999. ...
Na trasi avtoceste so na dnu morfoloških depresij oziroma uval med kraškimi pojavi najbolj vidni požiralniki in estavele. Pri gradbenih delih so se razkrile tudi podtalne škraplje ter jame. Izjemnih oblik so tiste, ki so nastale v dnu podolij in ki jih podtalne vode pogosto poplavijo. Imajo povsem svojevrsten, kot vemo tokrat prvič opisani skalni relief. Stare jame, skozi katere so se nekoč pretakali vodni tokovi, pričajo o znižanju gladine podzemeljske vode, ki površje dosega le v najnižjih podoljih ter o verjetnem tektonsko pogojenem členjenju kraškega površja. Dobršen del jam je zapolnjen z drobnozrnato naplavino in pod njo tudi preoblikovan. Oblikovanje špranjastih jam, ki so večinoma ob navpičnih razpokah, pa bi lahko opredelili kot podtalno. Razkrivajo se nam značilnosti plitkega in z naplavinami pokritega krasa, kjer je podzemeljska voda blizu površja. Te značilnosti bi bilo potrebno kar v največji meri upoštevati pri nadaljnjih poseganjih v kras, saj so nam na prvi pogled skrite, vsakršno poseganje v kras pa nam jih razkrije. Mnogi kraški pojavi predvsem jame, podtalne škraplje ali kamniti gozdovi so vredni, da jih zaščitimo in ohranimo.
The most conspicuous karst formations uncovered at the bottom of morphologic depressions or uvalas along the motorway route include swallow holes and estavelles. Also uncovered during the construction were underground karrens and caves of exquisite shapes, situated at valley bottoms and often flooded by groundwater. They have a specific rock relief that, to the best of our knowledge, is now described for the first time. Old caves through which streams were once flowing testify to the lowering of the level of groundwater, which reaches the surface only in the lowest-lying valleys, and to probable tectonic dissection of the karst surface. A good part of the caves are filled with fine-grained sediment and have been transformed underneath it. The shaping of fissure caves, located predominantly along vertical fissures, can be defined as having occurred subterraneously. They exhibit features of a shallow, sediment-covered karst where groundwater is close to the surface. These features are not visible at first sight, but they become apparent at any encroachment on karst and should therefore be taken fully into account in any such activity in the future. Many karst formations, above all caves, underground karrens or stone forests, are worthy of protection and preservation
... Denudation rates in karst areas measured by exposure of rock samples can be as high as 300 μm/yr, depending if rocks are subaerially or subsurface exposed to natural environment (e.g., Gams, 1985;Zhang et al., 1995;Audra and Pavuza, 2004;Dreybrodt, 2004;Plan, 2005;Krklec et al., 2013). Denudation is a very important process for the evolution of cave systems, leading to collapse of ceilings above shallow cave galleries, formation of unroofed caves and potentially modifying the microclimate dynamic of connected cave galleries (e.g., Mihevc et al., 1998Mihevc et al., , 2010Knez and Slabe, 2002;Domínguez-Villar et al., 2010). However, there is a limited literature on this topic (Mihevc, 1996(Mihevc, , 1998Mihevc and Zupan Hajna, 1996;Mihevc et al., 1998Mihevc et al., , 2010Geršl et al., 1999;Mais, 1999;Šebela, 1999;Slabe, 1999, 2002;Klimchouk, 2005). ...
... Surface streams are rare in karst regions with significant cave systems. Exposure of former cave passages or chambers after collapse of their ceiling is usual in shallow or ancient cave systems (e.g., Mihevc et al., 1998;Knez and Slabe, 2002;Mihevc et al., 2010). In these cases, denudation due to weathering becomes relevant to understand the evolution of the cave system. ...
We buried rock tablets of known weight in the soil of a karst region in Central Spain to evaluate the carbonate weathering during a period of a year. The experiment was conducted at two different soil depths: 5-10 and 50-55 cm from the surface. The parental rock used in the experiment is composed of dolomite and magnesite with variable proportion of accessory minerals and minor elements. Soil mineral and chemical composition as well as its texture was also characterized. Meteorological conditions at the site together with temperature and CO2 in both soil levels were monitored. Sets of tablets were retrieved after 6 and 12 months of the start of the experiment to account for seasonal weathering. Different lithologies do not have significant differences in weathering, although a large inter-sample variability is attributed to variable size and distribution of the porosity. Results show an enhanced weathering during the wet and cold season that accounts for 78 ±1% of the total annual weathering. Rock tablets examined under scanning electron microscopy prior and after exposure to natural environment show that most of the material lost occurred along cracks, edges or large porous. Although dissolution is a common process, most of the weathering is due to crystal detachment. Rock tablets at the depth of 5-10 cm were weathered 68 ±1% more than those set at 50-55 cm from the surface. Higher soil moisture and concentration of CO2 were found deeper in the soil, which likely enhanced the dissolution of carbonate. However, physical weathering dominated weight loss of rock tablets at both soil depths; especially at the 5- 10 cm level where soil thermal and moisture cycles were more frequent and ample. Denudation rate calculated from the 12 months set provides values of 2.48 ±1.07 m/yr and 1.75 ±0.66 m/yr at the depths of 5-10 and 50-55 cm respectively. Since the conditions at the average contact between soil and bedrock are similar to those at the 50-55 cm depth, we consider that this is a more reliable denudation rate for the studied location during the studied period. The calculated weathering rate suggests that denudation has a limited contribution to the thinning of bedrock over caves at this site. Therefore, we consider that the formation of unroofed caves in this region most likely results from the thinning of bedrock cover over caves due to collapse of blocks from their ceilings.
... The latter were of special interest to us because they proved to be a more common karstic phenomena than was thought before they were exposed (Fig. 1). We also identified their characteristic forms (MIHEVC et al., 1998;KNEZ & SLABE, 2001, to be published). This paper is an overview of experience gained in past years of research into this interesting karstic phenomenon. ...
... The landforms of unroofed caves, which include dolina-like landforms, series of such landforms and oblong depression (KNEZ & SLABE, 2001, to be published), are the consequence of cave forms and the development of the relief above them. The relation between the speed of sediment removal from the cave and the lowering of the surrounding relief determines how discernible these landforms are. ...
Old caves are being exposed due to lowering and dissecting of a karst surface. The surface either uncovers or intersects them. In the first case the unroofed caves display the form of an oblong indentation and in the second a doline-like feature. Repeatedly intersected passage is shown as a series of described features. The most expressive are these features when the transport of sediments out of the caves is faster than the lowering of the nearby carbonate surface. A bigger cave system near Kozina indicates a diversity of exposing types. A smaller and already vacant passage was known before the earth works for motorway construction started. Other passages were filled up by fine-grained and gravel flysch deposits. Some of them have a thin roof other were roofless already. At the surface parts of a cave system are seen as a system of different indentations and doline-like features.
... Geomorphologically it can be defined as a mature karst, as evidenced by the density of karst features such as caves and dolines (Gams, 1993;Knez and Slabe, 2002;Blatnik et al., 2020). This intense karstification, along with the scarce presence of surface deposits (Fig. 3), favours the effective infiltration to the aquifer (Savi et (Jurkovšek et al., 2016, cfr. ...
... They present the former underground features that are now exposed on the surface [1], [2]. Depending on the cave type and the manner in which denudation cut the cave, the unroofed caves appear as elongated dolines, series of dolines, shafts or linear to irregular depressions completely filled with sediments [2] - [4]. The term unroofed cave also includes flowstones and other allochthonous fluvial cave sediments that appear on the surface, even when caves are not morphologically expressed due to strong surface reshaping [2]. ...
Ground penetrating radar (GPR), a non-destructive geophysical method, was used to detect cave sediments, now exposed on the karst surface (in so-called “unroofed caves”) due to a general lowering of the surface (dissolution of carbonate rocks). It turned out that cave sediments are expressed as areas with strong signal attenuation on GPR radargrams. In order to test the GPR’s capability and reliability in detecting cave sediments, further mineralogical-geochemical analyses were conducted to reveal which factors influence the attenuation the most. At the testing location, samples of cave sediments and soils on carbonate rocks were taken for X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses to compare the mineral and geochemical compositions of both sediments. Results show that cave sediments contain higher amounts of clay minerals and iron/aluminum oxides/hydroxides which can strongly affect GPR penetration. Differences in the mineral composition also lead to water retention in cave sediments even through dry periods which additionally contribute to increased attenuation with respect to surrounding soils. Based on these findings, GPR profiling was used on several other places where direct indicators of unroofed caves are not present due to strong surface reshaping. GPR has proven to be a reliable method for locating these areas and can be a valuable complementary method to geological mapping for a more comprehensive recognition of unroofed cave systems. These are important for understanding karst erosion processes and geomorphology. For instance, studying unroofed cave systems can help with reconstructing the direction of former underground water flows.
... Studies of the karst characteristics of Minamidaito Island were undertaken in the framework of a grant-in-aid project for the Scientific Research Program of the Ministry of Education, Science, Sports, and Culture of Ja- MARTIN KNEZ, TADEJ SLABE & KAZUKO URUSHIBARA-yOSHINO pan and the Karst Research Program (Slovene Research Agency) of Slovenia. Part of the project was devoted to broadening knowledge about the development of the island's karst (preliminary information was prepared for the local conference, Knez et al. 2013), augmented with a study of lithomorphogenesis, part of the global study of the formation of karst surfaces given diverse rock, conditions, and different regional frameworks (Knez & Slabe 2002;Debevec et al. 2012;Al Farraj Al Ketbi et al. 2014;Gutiérrez Domech et al. 2015;Knez et al. 2011Knez et al. , 2012Knez et al. , 2015Slabe 2005Slabe , 2009Slabe et al. 2016;and, Karst Rock Features book (Ginés et al. 2009). A variety of characteristics of the formation and development of karst features is clearly evident. ...
Minamidaito Island is a karstified coral island located on the Philippine plate. Karstification periods occurred during the end of the Pliocene, in major part of the Pleistocene, and in the Holocene. The first period of karstification can be observed in the lower Daito dolomitized limestone (5 Ma and 4 Ma); the karstification seems to have occurred as a result of sea level change caused by the cooler conditions of the paleoclimatic environment. Geological studies were performed to study reef carbonates in detail. Among them, biointrasparite limestone of framestone and bafflestone types with transitions to grainstone and dolomitized biointrasparry limestone of framestone and bafflestone types dominate. Calcimetric analyses established that in certain locations the distribution of limestone and dolomite differs from the distribution previously described. Rock relief reveals the unique formation of coastal karren, the development of the surface in the interior of the island, and the most characteristic periods of cave development.
Key words: Minamidaito Island, lithlogy, coral dolomitized limestone, rock relief, coastal karren, karstification, vegetation.
... In the north-western portion of the summit palaeosurface (S1), at about 1450 m a.s.l. we recognized a particular karst landform identified as roofless cave or unroofed cave (Mihevc & alii, 1998;Knez & Slabe, 2001), partially transformed by surface processes (fig. 6). ...
With more than 250 caves, the Alburni Mts represent one of the most important karst areas of southern Italy. The backbone of this ridge is constituted of Mesozoic-Cenozoic limestone with limited outcrops of Miocene siliciclastic formations and internal shale units, often trapped in elongated downthrown structures. NW-SE- and NE-SW-trending faults with a clear morphological expression are responsible for the genesis of a squared framework of flat-topped ridges and flat-bottomed valleys at the top of the massif. In an approximate way, the Alburni Mts can be described as a roughly NW-SE-trending monocline, dipping toward the SW, covering an area of about 350 km2. The fault system has partially disrupted an ancient flat landscape, as testified by the widespread fragments of the southern Apennines late Pliocene - early Pleistocene summit palaeosurface. This work aims at understanding the role played by tectonic structures on karst development based upon a morphometric analysis. We also try to constrain the age of the karst phenomena using the relationships among morpholineaments, land surfaces, and other morphotectonic markers. New data, besides confirming the role of the map-scale faults as a controlling factor of the surface and hypogean karst development, also highlight the strong influence of the small-scale faults and pervasive jointing. Further, the presence of different levels of hypogean karst seems to trace the arrangement in several orders of land surfaces, thus suggesting a discontinuous lowering of the (relative) erosion base level due to a multi-phase tectonic uplift.
... In the north-western portion of the summit palaeosurface (S1), at about 1450 m a.s.l. we recognized a particular karst landform identified as roofless cave or unroofed cave (Mihevc & alii, 1998;Knez & Slabe, 2001), partially transformed by surface processes (fig. 6). ...
With more than 250 caves, the Alburni Mts represent one of the
most important karst areas of southern Italy. The backbone of this ridge
is constituted of Mesozoic-Cenozoic limestone with limited outcrops of
Miocene siliciclastic formations and internal shale units, often trapped in
elongated downthrown structures. NW-SE- and NE-SW-trending faults
with a clear morphological expression are responsible for the genesis of a
squared framework of flat-topped ridges and flat-bottomed valleys at the
top of the massif.
In an approximate way, the Alburni Mts can be described as a roughly
NW-SE-trending monocline, dipping toward the SW, covering an area
of about 350 km2. The fault system has partially disrupted an ancient
flat landscape, as testified by the widespread fragments of the southern
Apennines late Pliocene - early Pleistocene summit palaeosurface.
This work aims at understanding the role played by tectonic structures
on karst development based upon a morphometric analysis. We
also try to constrain the age of the karst phenomena using the relationships
among morpholineaments, land surfaces, and other morphotectonic
markers.
New data, besides confirming the role of the map-scale faults as a
controlling factor of the surface and hypogean karst development, also
highlight the strong influence of the small-scale faults and pervasive
jointing. Further, the presence of different levels of hypogean karst
seems to trace the arrangement in several orders of land surfaces, thus
suggesting a discontinuous lowering of the (relative) erosion base level
due to a multi-phase tectonic uplift.
... On t�e surface, t�e most relevant landforms in terms of deep karstification are dolines. Their morp�ometry �as been analysed (maximum, minimum and medium diameter, dept�, plan s�ape, s�ape of slopes, filling material and s�ape of bottom) in order to detect t�eir genesis (solution doline or collapse doline, unroofed cave) and t�eir dept� (Andriani et al. 2001;Knez & Slabe 2005;Mi�evc et al. 1998;Mi�evc 1999;Slabe 1997;�ušteršič 1994). ...
Val Rosandra is a unique geomorphological environment located on the western side of the Classical Karst Plateau (NE Italy). This deep limestone gorge is crossed by a stream that is fed by a large basin located in Slovenia. Val Rosandra is the only example of a karst river valley with surface hydrography in the Classical Karst Plateau. The torrent that crosses it digs a deep gully into the rock, rich in rapids, swirl holes, small waterfalls, enclosed meanders and basins; here, the first seepage phenomena occur, and part of the water feeds the underground aquifer.Val Rosandra is characterised by a complex structural situation. The NE slope culminates in the structure of Mt. Stena, a limestone tectonic wedge between two faults, firmly rooted in the karst platform. Both its external morphology and its caves are influenced by the structure, i.e. by the attitude of bedding planes, fault planes and master joints. Mt. Stena, in particular, hosts a comprehensive net of articulated and diversely shaped caves, basically organised on several levels. This network stretches over a total of 9,000 metres, bearing testimony to ancient geological and hydrogeological origins.The deepest areas of the system reach a suspended aquifer that is probably sustained by an overthrust and placed about 100 meters above the underground aquifer of the Rosandra torrent.A series of feasibility studies on the Trieste-Divača high-speed railway link concentrated on the potential interaction between the project and karst features. In line with the project requirements, risk of voids intersection and water contamination were analyzed as Mt. Stena's suspended aquifer partially feeds the Rosandra torrent, which flows in a protected natural area. we therefore suggest that further investigations ought to be performed to integrate the existing knowledge on karst and on the hydrogeological aspects of the massif.
... Almost one-third of the caves newly discovered on road projects are unroofed caves (Knez and Slabe, 2002a). These are old cave passages that became exposed by lowering of the karst surface, so that they have now lost their roofs. ...
... Frequentemente le acque meteoriche dilavano i sedimenti in esse contenute e questo giustifica il fatto che la maggior parte delle roofless cave si presentano in superficie come depressioni assimilabili alle doline. La presenza di queste morfologie, in assenza di depressioni, è talvolta rivelata dall'affioramento di concrezioni nelle tipiche forme che si rinvengono nelle attuali cavità (colate calcitiche, stalagmiti, gours, ecc...) (Mihevc, 2007;Mihevc et al., 1996Mihevc et al., & 1998Šebela, 1999;Knez et al., 2005). ...
... Therefore, a more probable explanation would be that these closed depressions were caves in the past, most probably inner shafts such as those in the Alps or High Dinaric karst plateaus such as Trnovski gozd (shafts in Velika ledena jama v Paradani described by Mihevc (1995)). These shafts were then uncovered by surface denudation and exposure to superficial conditions, as is seen in innumerable examples from Classical karst (Mihevc, 1996; Mihevc, Zupan Hajna, 1996; Mihevc, 1998a Mihevc, , 1998b Mihevc, , 1999a Mihevc, , 1999b Mihevc, , 1999c; S ˇ ušteršič, 1999; Mihevc et al., 2002; Knez and Slabe, 2002; Mihevc, 2006 Mihevc, , 2007). Mihevc (2001) described such cases with examples from Divaški karst, where denudation of the karst surface exposed caves and their contents to the surface. ...
On the southern slope of Dedna gora, Slovenia, at an elevation of 1147 m, an interesting large closed depression referred to as Barka (Barge) is developed. It is about 40 m long, 25 m wide and 20 m deep, with smooth, almost polished precipitous walls. It is developed in Upper Cretaceous limestones and affected by several faults and fissure zones. The feature lies within a large karren field (about 104 m2) with many closed depressions of various dimensions. In the winter time, snow accumulates in the bottoms giving the appearance of snow-kettles, such as those found in the Alps. The size and especially the shape of the walls suggests that these features are the remains of shafts. After their primary genesis as the inner vadose shafts of one or more caves, their upper parts would have been denuded. Walls and bottoms were subsequently remodeled by snow and ice action during the last glaciations, and this continues today as winter snow accumulates at their bottoms. This is indicated by silt fragments (gelifraction) and frost rubble accumulated in portions of the depression, and the development of sorted and nonsorted polygons. Shafts that have been exposed at the surface are a potentially important morphological element of karst topography. They can represent a significant portion of closed depressions of different sizes, including many snow-kettles.
... Karstologists have been directly involved in the planning, construction and operation of the Slovene motorways through the Classical Karst (Kras) region since 1970 (Kogovšek 1993;Knez and Š ebela 1994;Š ebela and Mihevc 1995;Slabe 1996Slabe , 1997aSlabe , b, 1998Mihevc and Zupan Hajna 1996;Mihevc 1996Mihevc , 1999Kogovšek et al. 1997;Mihevc et al. 1998;Š ebela et al. 1999;Knez et al. 1994Knez et al. , 2003Knez et al. , 2004Bosak et al. 2000;Knez and Slabe 2001, 2002, 2005. More than 350 caves have been discovered in the course of building 60 km of new motorways over the past decade. ...
Karst researchers of the Karst Research Institute ZRC SAZU are regularly consulted during the planning of Slovenia’s motorways
and invited to observe and monitor construction in the karst areas. More than 350 caves have been discovered in the course
of building 60km of new motorways over the past decade. Access to the most important caves is preserved by concrete tubes
closed with metal covers at the roadside. The largest cave system in a tunnel, named LC-S647, is almost entirely preserved.
The protection of this cave will serve as a good example for the preservation of natural heritage in the future. Construction
work for the motorway uncovered a high degree of karstification. In particular, the discovery of this cave in the Kastelec
tunnel LC-S647 showed the existence of a major cave system in the geological and speleological past. A number of unconnected
passages have also been found. Caves discovered during highway construction have brought new knowledge about the cavernosity
and the geological history of this part of the karst.
According to origin, karst caves are, of course, an underground phenomenon, but in the development of the karst, they frequently appear as surface phenomena that we call “unroofed caves”. Due to the denudation, dissolution and disintegration of carbonate rock and the subsequent lowering of the karst surface, which can be many dozen metres in a million years, underground karst caves are uncovered and with further dissolution can gradually disappear completely. Here we show the frequency, significance and characteristic forms of unroofed caves and place them correctly in the development scheme of the karst cycle. Many years of research of the Classical Karst in Slovenia have shown that unroofed caves are a relatively frequent surface karst form, certainly more frequent that we imagined before expressway construction works in Slovenia’s karst regions uncovered the karst surface. The first attempts to typify their characteristic forms and to explain their formation were born. Our results show the development from old caves to unroofed caves due to the lowering and dissection of the karst surface. Old caves are preserved by sediments, primarily alluvium and flowstone. We present forms of unroofed caves and determine their significance in studying the cavernosity of karst aquifers.
The leading role of dissolution and the dominant subsurface drainage determine the special idiosyncrasy of karst geomorphology, with some notable variations depending on the type of soluble rock. The formation of karren is essentially related to the uneven or differential dissolution of the bedrock surface controlled by a number of factors, resulting in the development of depressions, clefts, channels, tubes, protruding features, and irregular patterns. Sinkholes or dolines are enclosed depressions with internal drainage widely regarded as one of the most characteristic landforms of karst landscapes. They are typically circular to subcircular in plan and show wide morphological diversity (cylindrical‐, conical‐, bowl‐, and pan‐shaped). In some cases, the variable geometry of the sinkholes can indicate different evolutionary stages and the relative age of the depressions. In nature, a complete spectrum between suffosion, collapse, and sagging sinkholes can be found in covered karst settings.
By the geomorphologists, karst had been traditionally observed as a type of relief due to the inaccessibility of underground features [1]. The findings of hypogene karst provoked the ideas that karst system may not necessarily reflect in the landscape [2]. The recognition of karst denudation and its crucial role in surface morphology revealed the inseparable correlation of karst relief to speleogenesis [3, 4]. High diversity of karst features as a consequence of not completely developed karsts (in the sense of [5] around the world has led to localized studies instead of solving basic and general questions of karst and karstification. To overcome this obstacle, Šušteršič (o.c.) developed “The Pure Karst Model” by which he visualized fundamental processes of karstification resulting in basic geomorphic elements of karst surface: centrally organized depressions and intermediate elevations.
Krk Island is one of the largest Croatian islands, occupying an area of 405.5 km².
This paper details methods that contribute towards solving the problem of the spatial relations between surface and underground karst morphology - relationships that are often unclear. The karst landforms studied in this context are karst valleys, through-caves and natural bridges. Two study sites are situated in the Carpatho-Balkan Mountains of eastern Serbia: the dry valley of the Radovanska Reka River on Mt Kučaj (together with the Pećura through-cave) and the Zamna Cave in the wider area of the Danube Gorge. The caves and the closest adjoining parts of the valleys were measured in detail using the terrestrial laser scanning method. The data obtained showed that some previous measurements at these locations, performed with classical traditional instruments, are insufficiently accurate and may lead to wrong conclusions.
All ground voids constitute elements of weakness within a rock mass, and karst is distinguished by having the largest natural voids, where roof failure can create a significant geohazard. The natural consequence of progressive roof failure is upward void migration, which may reach the surface where it causes instantaneous major subsidence in the form of a collapse sinkhole. Where the roof failure migrates up through non-karstic rocks, the surface failure in an outcrop of insoluble rock creates a caprock sinkhole. Both these forms of sinkhole involve failure and collapse of bedrock, and are therefore distinct from the subsidence sinkholes where soil cover is flushed into stable rock fissures (Chapter 4).
The vast majority of ground failures within karst terrains are due to the erosion, transport and failure of the soils that overlie cavernous bedrock. Dissolution and removal of enough limestone to form a cave of significant size requires geological timescales that cover tens of thousands of years. In contrast, a comparable volume of soil can be removed during a single rainstorm, where there is a stable, old karstic cave somewhere beneath that can accept the displaced material. The rock left over a limestone cave is generally strong enough to stand for very long periods of time. In contrast, a soil arch over any void is inherently unstable, and may fail immediately or during a subsequent rainstorm. For these two reasons, soil failures are much more common than rock failures in karst. The chances of an engineered structure being damaged or destroyed by sinkhole development due to soil failure, during its design lifetime, are orders of magnitude greater that the chances of rock collapse.
An ever-present geohazard in karst terrains is the collapse of bedrock into open caves when engineering works inadvertently impose new loadings on the unsupported spans over unknown caves. However, rock collapse is a rare event. A scatter of collapse and caprock sinkholes exist across most karst terrains (Chapter 3), but their small numbers have developed through geological time, albeit without imposed loading. Nearly all collapses induced by engineering activity in karst are subsidence sinkholes that develop entirely within the soil profile (Chapter 8). Induced rock collapse may be rare, but events can be catastrophic and should be avoided by appropriate engineering design.
Design and construction of buildings and infrastructure in karst terrains are influenced not only by the character of the bedrock but also by the nature and thickness of the soil cover. Voids and cavities in both the bedrock and the soil are significant as potential sites for collapse. The possibility of subsidence due to them, whether slow or rapid, therefore has to be assessed prior to the commencement of construction operations. Hence construction must involve the total environment that influences those processes that aggravate sinkhole development in karst and its overlying soils, both on-site and in the immediate environs (Sowers, 1996ref). Once an assessment has been made, it may be possible to change the layout of a site to avoid the potential hazards. Ground preparation on sites within karst terrain can include remedial work on existing sinkholes and dissolution features, and also works to prevent or minimise the impact of their future development. Landfills on karst provide a special case where the nature and behaviour of the cover soils is critical; any potential hazard of new sinkhole development beneath landfill threatens its integrity with the added risk of serious pollution of local groundwater resources.
Deep-seated gravitational deformations are significant denudational agents of rock slopes at the margins of karstified plateaus of the Crimean Mountains (CM). The CM evolved during Mesozoic–Cenozoic times as a response to the deformation between the Black Sea domain and East-European platform. The southwestern part of the area is characterized by steep, up to 1000-m-high coastal escarpments consisting of Late Jurassic limestones overlying tuff layers and weak Late Triassic flysch with sporadic small intrusions of Middle Jurassic diorites, gabbros and granites. Steep rock slopes contrast with elevated, highly karstified plateaus situated approximately 500–1300 m a.s.l. The aim of this article is to show long-term evolution of a giant rock slope failure close to the Black Sea coast in the southwestern tip of the CM near Foros Town. The failure evolved in highly anisotropic limestones overlying plastic flysch layers where the main head scarp follows a strike-slip fault. The Foros slope failure is an excellent demonstration of the significance of a preparatory stage in the evolution of large deep-seated slope deformations. Inherited and undisturbed horizontal slickensides on the sub-vertical, inactive fault surface serve as good evidence of significant extensional movement of the surface blocks away from the main headscarp. The studied deformation shows that in a relatively small area tensional (cutting) surfaces can be formed by a great variety of rock discontinuities such as the strike-slip fault, joints and steeply inclined bedding planes. The presence of well-developed, nowadays weathered, speleothems furthermore points to significant karstification that provided additional widening of spaces within rock mass. Gravitational movement destroyed and unroofed several cave systems originally presented at the former edge of a karst plateau. Our findings reveal that large rock slope failures can be added to the factors contributing to the evolution of unroofed caves. Although triggering factors of the activation of individual parts of slope deformations can be determined only hypothetically, lessons learned from widespread landslide activity during and after the 1927 Yalta earthquake and rainfall-driven landslides in the vicinity of Feodosia Town make us consider both seismic loading of slopes and high pore-pressures during heavy winter rainfalls or rapid spring snowmelt to be significant factors. Beside seismic activity, intensive Late Holocene slope processes can be attributed to intensive human activity.
One of the major ongoing projects in Slovenia was to link the country with modern motorways. Almost half of Slovenia is karst and more than half of its supply of water comes from karst aquifers. Slovenia is the home of the Classical Karst region - Kras. Karstologists have been involved in planning and construction ofmotorways. We have acquired a great deal of information about surface karst phenomena and the epikarst, and where excavation work has cut deeper in the surface and in tunnels, about the vadose zone and the paleokarst. Development of the karst usually left important traces, above all in the numerous old caves. More than 350 new caves have been opened. During the planning we tried to avoid important karst phenomena as are collapse dolines, large dolines, caves and karst walls and by impermeable construction of a roadway we tried to prevent the pollution flowing from it into underground waters. During the construction works we researched newly discovered karst features and tried to preserve as many as possible.
The age of a karst can be defined as the time when the karst rocks were uplifted out of the sea. The other view of the age of karst is to define the age of certain karst features or assemblages of karst features. On the Kras plateau there is a variety of forms that were formed at quite different times, but due to karst evolution, they coexist in todays relief. On the plateau, that is slowly rising, the hydrological zones in karst surface are moving downwards. Streams from the side ceased to flow on the karst and former leveled surface that was formed in conditions of high ground water is dissected by numerous dolines. Blind valleys are incised at the side and some of them show the influence of recent tectonics. The lowering of relief by corrosion exposes caves that have formed deep beneath the surface and creates unroofed caves that become a part of the surface topography. From the morphological comparison of the unroofed caves, blind valleys and levelled surfaces and by dating of the sediment and considering the age of tectonic phases we can reconstruct the evolution and estimate the age of the karst landscape.
The marble caves of the Central Scandinavian Caledonides were formed from open fractures that were created primarily by deglacial seismicity at the culmination of each of the many complex Quaternary glaciations that the region has experienced. Subsequent inundation by deglacial ice-dammed lakes enabled phreatic enlargement by dissolution, with passages either becoming relict during the following interglacial or else being entrenched by (mainly) vadose processes if recharged by allogenic streams. Because the distance of the contemporary fractures and therefore the cave passages from the nearest land surface is commonly constrained to be less than one-eighth of the depth of the local glaciated valley, the caves are rather epigean in nature. This subsurface cave distance is of the same order of magnitude as the thickness of rock removed from valley walls and floors at each major glaciation, suggesting that, when viewed over several glacial cycles, caves are involved in a race to develop deeper during déglaciation and the following interglacial before their upper levels are removed by erosion at the next glaciation. Indeed, relatively few cave passages in the study area can have survived from the previous, Eemian, interglacial. This paper examines evidence for the interglacial and erosional processes and utilises a 'black box' approach to provide an external model for cave development and removal. It proposes that Caledonide marble caves in stripe karst outcrops should especially be considered as four-dimensional objects throughout their commonly intermittent existence. Mainly vadose caves are regarded as 'half-cycle' caves that developed primarily in the Holocene. Relict caves (primarily phreatic) and combination caves (with both phreatic and vadose elements) are commonly 'single-cycle' caves that developed their relict phreatic passages during Weichselian deglaciation, and only a few are 'multi-cycle' caves that have experienced several Pleistocene glacial cycles. The existing caves are more numerous and commonly larger than those that were present during previous interglacials.
Stalactitic deposits of calcium carbonate are often seen on cliffs and in other epigean settings in the tropics. Since it is generally accepted that the formation of stalactites requires the enclosed atmosphere of caves, such deposits at the land surface are often considered decayed speleothems, remnants of former caves breached by erosion and collapse. However, our sampling of stalactites from epigean settings in the Mariana Islands, Western Pacific, has revealed that they belong to at least two distinct categories of deposits, which exhibit a superficially similar form and structure but have profoundly different depositional histories and are not necessarily related to former caves. We have termed them exposed stalactites and stalactitic tufa. The former are hard, densely layered, coarsely crystalline calcite deposits that formed as true speleothems and subsequently became exposed at the land surface. They indeed are indicators of dissolutional landforms and former caves. The latter, however, are subaerial deposits of calcareous tufa, which convincingly mimic speleothems but actively grow in humid epigean settings. They are contemporary parts of the land surface environments in which they are observed and cannot be used to indicate de-roofed, intersected, or otherwise exposed spelean environments.
A proposed railway on the 5th European Railway Corridor (Venice-Kiev) between the northern Adriatic ports of Koper (Slovenia) and Trieste (Italy) and the interior of Slovenia required extensive karstological studies and planning. This book contains the knowledge gained from these studies as well as further information on the regional karst surface and underground, the karst hydrogeology and the specific caves of the Beka-Ocizla cave system.
Base-level lowering plays an important role in cave passage development and morphology. Cave conduits are commonly formed at depth below the water table, and subhorizontal conduits can form at depths of more than 100 m below the water table. Subsequent base-level lowering is responsible for evolution from a deep phreatic to a shallow phreatic to a vadose, water table setting. Most caves do not evolve to a vadose passage stretching from sink to spring because the flow is captured by undercaptures: passages at a lower elevation and below the water table. Undercaptures provide much of the complexity seen in cave maps. Distributary springs and bypass passages can also be formed during short-term rises in base level that also produce wall notches.
The Inception Horizon Hypothesis of cave origin encompasses geology-centred views of when, why and how primitive permeability was imprinted within mainly karstic limestone sequences. Potentially, the earliest processes affect unconsolidated or partially consolidated sediment during early diagenesis and are inevitably related to lithological contrasts. Such contrasts eventually become recognizable as specific horizons, to the extent that these 'inception horizons' become an intrinsic part of the preserved rock succession during syngenetic and mesogenetic diagenesis. The horizons provide the key to the establishment of the earliest extended, low efficiency hydraulic gradients within rocks that were initially virtually impermeable. With the onset of telogenetic conditions following uplift and tectonism the early role of 'inception horizons' continues under less confined or unconfined conditions, but with added scope for the involvement of tectonic fractures (broadly faults and joints). These can provide 'inception links', enabling establishment of geometrically more complex but also more efficient hydraulic gradients. Whereas a newly uplifted karstic succession can include the imprints of several vertically-stacked 'inception horizons' linked to depositional cyclicity (sensu lato), how these imprints help to guide aspects of later cave development depends upon the three-dimensional relationships of'inception horizons' and 'inception links' (folds and fractures) and upon how the developing landscape interacts with them. The still partly theoretical concept is illustrated with examples from the Yorkshire Dales.
Deep-seated gravitational deformations are significant denudational agents of rock slopes at the margins of karstified plateaus of the Crimean Mountains (Ukraine). The aim of this article is to study long-term evolution of a giant rock slope failure close to the Black Sea coast in the southwestern tip of the mountains near Foros Town. The failure evolved in highly anisotropic limestones overlying plastic flysch layers where the main headscarp follows a strike-slip fault. We tested a new chronological strategy based on 14C and U-/Th-series dating of speleothems from unroofed caves exposed in the headscarp area of the slope failure. This approach made it possible to state maximum age of the slope collapse in individual parts of the deformed slope. Obtained results indicate that extension of discontinuities together with their karstification can be traced to > 300 ka BP, whereas evolution of the main headscarp started ~ 110 ka BP and since then it has propagated in the eastward direction. The youngest slope failure in the easternmost part of the studied collapse is of Late Holocene age. Our study indicates that conditions for large rock slope failures in carbonate areas can be prepared by speleogenesis or combined effects of propagation of cracks and their solution-based expansion. Furthermore, large rock slope failures can be important factors for the genesis of unroofed caves.
Major motorway construction is taking place in Slovenia. Almost half the country is karst and many of the new roads are in
such terrain. Karst specialists are involved in road design. They explore underground karst systems and suggest how best to
preserve the most important ones. These experts also provide advice on ways of protecting karst groundwater and on aspects
of road construction in karst. The karst features encountered during construction provide valuable information about the development
of karst systems.