LABORATORY MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER: SUBSOIL KARREN, RAIN FLUTES KARREN AND CAVES


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LABORATORY MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER: SUBSOIL KARREN, RAIN FLUTES KARREN AND CAVES

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LABORATORY MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER: SUBSOIL KARREN, RAIN FLUTES KARREN AND CAVES
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Acta Caroslogica
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Slabe, Tadej
Hada, Asami
Knez, Martin
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English; Slovenščina

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Laboratory Modeling ( local )
Karst ( local )
Rock Relief ( local )
Subsoil Karren ( local )
Rain Flutes ( local )
Caves ( local )
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serial ( sobekcm )

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The study of the formation and development of karst phenomena and their rock relief using laboratory plaster modeling has again proven useful and informative. We continued the study of subsoil karren that forms under tight, poorly permeable contact with soil and of rain flutes formed by water at various temperatures. We determined the pattern of the reshaping of plaster tubes that are wider at the flow inlet than at the outlet end. The results are a significant contribution to explaining the formation of high ceiling niches and pockets in karst caves. The third experiment was carried out in phreatic conditions where water in a flume was forced to flow between layers of different composition. During the experiment, we observed the typical development of channels between pure plaster layers (uniform limestone beds), between plaster layers with added Portland cement reinforced fragments (breccia beds), siporex (slowly dissolving beds) and between three different layer types.
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Acta Caroslogica, Vol. 45, no. 2 (2016-11-30).

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LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN FLUTES KARREN AND CAVES LABORATORIJSKO MODELIRANJE KRA KIH POJAVOV IN NJIHOVEGA SKALNEGA RELIEFA NA MAVCU: PODTALNE KRAPLJE, DEtNI tLEBI I IN JAME Tadej SLABE 1, 2 , Asami HADA 3 & Martin KNEZ 1, 2 Izvleek UDK 911.2:551.435.8 Tadej Slabe, Asami Hada & Martin Knez: Laboratorijsko modeliranje krakih pojavov in njihovega skalnega reliefa na mavcu: podtalne kraplje, deni lebii in jame Prouevanje oblikovanja in razvoja krakih pojavov in njihove ga skalnega reliefa z laboratorijskim modeliranjem z mavcem se je spet izkazalo kot koristno in povedno. Nadaljevali smo s prouevanjem podtalnih krapelj, ki se oblikujejo pod tesnim, slabo prepustnim stikom s prstjo in denih lebiev, ki se obli kujejo z vodo razlinih temperatur. Razbrali smo nain obliko vanja mavnih cevi, ki so ire na pritoni kot odtoni strani. Izsledki so pomemben prispevek k razlagi oblikovanja visokih stropnih ni in kotlic v krakih jamah. Tretji poizkus smo izvedli v freatinih pogojih, ko se je voda pretakala med plastmi razline sestave. Opazovali smo znailen razvoj kanalov med ploami istega mavca (apnenasta plast), med ploami ma vca z dodanimi in s cementom uvrenimi poasneje topnimi klasti (brea), siporeksom (slabo topna kamnina) in med tremi razlinimi ploami. Kljune besede: laboratorijsko modeliranje, kras, skalni relief, podtalne kraplje, lebii, jame. 1 Karst Research Institute, Research Centre of the Slovenian Academy of Sciences and Arts, Titov trg 2, SI-6230 Postojna, Slovenia and UNESCO Chair on Karst Education, University of Nova Gorica, Glavni trg 8, SI-5271 Vipava, Slovenia, e-mails: knez@zrc-sazu.si, slabe@zrc-sazu.si 2 Y unnan University International Joint Research Center for Karstology, X ueyun rd. 5, CN-650223, Kunming, China, e-mails: knez@zrc-sazu.si, slabe@zrc-sazu.si 3 Nihon University, College of Commerce, 5-2-1 Kinuta, Setagaya-ku, Tokyo, Japan, e-mail: hada.asami@nihon-u.ac.jp Received/Prejeto: 13.07.2016 COBISS: 1.01 ACTA CARSOLOGICA 45/1, 187, POSTOJNA 2016 Abstract UDC 911.2:551.435.8 Tadej Slabe, Asami Hada & Martin Knez: Laboratory model ing of karst phenomena and their rock relief on plaster: sub soil karren, rain utes karren and caves e study of the formation and development of karst phenom ena and their rock relief using laboratory plaster modeling has again proven useful and informative. W e continued the study of subsoil karren that forms under tight, poorly permeable contact with soil and of rain utes formed by water at various temperatures. W e determined the pattern of the reshaping of plaster tubes that are wider at the ow inlet than at the outlet end. e results are a signicant contribution to explaining the formation of high ceiling niches and pockets in karst caves. e third experiment was carried out in phreatic conditions where water in a ume was forced to ow between layers of dierent composition. During the experiment, we observed the typical development of channels between pure plaster layers (uniform limestone beds), between plaster layers with added Portland cement reinforced fragments (breccia beds), siporex (slowly dissolving beds) and between three dierent layer types. Key words: laboratory modeling, karst, rock relief, subsoil kar ren, rain utes, caves.

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ACTA CARSOLOGICA 45/2 – 2016 188 T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ e modeling of karst phenomena and their rock forms and relief in plaster exposed to dierent factors in a vari ety of conditions has oen proved useful. e limitations and particularities of plaster modeling oen originate in the fact that in most cases the models are smaller than the original phenomena in nature and that more plaster dissolves (more than 2 g of plaster dissolves per 100 g of water at 20 C). e consequence of the latter is that the forms on plaster are typically smaller than those on limestone and their development cycle is much faster. According to our experience, however, they provide a very useful comparison. Modeling oers various possi bilities for the continuous monitoring of the origin and development of rock forms. W hile the modeling of a plaster block exposed to a ow of water or to rain can be monitored continuously, an experiment in the forma tion of subsoil karren must be repeatedly interrupted and renewed and the formation of rock relief in plaster tubes exposed to a water current can only be monitored using special instruments. W e continue with the studying the formation of subsoil karren and subsoil rock teeth (Slabe 2005, 2009; Slabe & Liu 2009), we tried to make clear the eects of water temperature on the formation processes of rain utes (Gins 2009; Slabe 2009), and continue with re search of the development of caves by exposing tubes of dierent diameters and a plaster block composed of dif ferent layers to a ow of water. Models are dierent, so the methods are presented in the beginning of each. INTRODUCTION PREVIOUS PLASTER MODELING E X PERIMENTS DESCRIBED IN THE LITERATURE Experiments in modeling have deepened our knowledge about cave rock forms. Rudnicki (1960), Curl (1966), Goodchild & Ford (1971), and Allen (1972) studied scallops with plaster models. Curl (1966) established beyond dispute that the length of scallops depends on the speed of the wa ter constantly owing over the rock; the size and shape of scallops is also inuenced by the size of the passage whose walls contain the scallops, the density and viscos ity of the water, ions diusion, and the properties of the rock where the scallops form. Goodchild & Ford (1971) studied the relationship between the size of scallops and the hydraulic conditions. Allen (1972) used experiments with plaster channels to demonstrate that scallops can form on rock whose component parts are large enough for the development of independent vortexes. e pres ence of non-homogeneous elements inuences the dis tribution of scallops and a single non-homogeneous ele ment can trigger the formation of scallop-like features. Quinif (1973) used a model to study the formation of ceiling pockets. He immersed a ssured block in wa ter and poured HCl through a ssure. A ceiling pocket formed at its bottom. Lauritzen (1981) studied the paragenetic transfor mation of a cave ceiling above ne-grained sediment us ing plaster modeling experiments. Ewers (1966, 1972, 1982) used salt models to study bedding-plane anastomoses. Experimental research (Slabe 1995a, b) on abovesediment ceiling channels and anastomoses in caves, below-sediment utes, dierent types of scallops and the impact of rock and hydraulic conditions on their size and shape, and ceiling pockets formed due to the perco lation of water through ssures contributed considerably to explaining their origin under dierent conditions and the diverse shaping of karst caves. Many experiments have been conducted on the for mation of karst surfaces and the rock forms on them. Pluhar and Ford (1970) studied the formation of utes by using hydrochloric acid on a dolomite block. Glew and Ford (1980) studied utes and rillenkar ren in experiments exposing plaster surfaces inclined from 22.5 to 60 to articial rain. ey established that utes form in places where a thin layer of water owing across an inclined surface does not block rain drops from direct contact with the rock. Under a thicker layer of wa ter, however, the surface of the rock becomes smooth. e length of utes is related to the inclination of the rock surface. Dzulynski et al. (1988) used modeling to study the formation of karren by exposing a ssured block of plas ter to articial rain. ey studied karren formed by rain water as well as subsoil karren. ey were interested in how the plaster is dissected by channels that form along ssures, how protrusions form between them, and how the level of water surrounding them aects their devel opment. ey determined that the amount of rain aects the speed at which the plaster dissolves but not the shape of the articial karren. e plaster covered with sand dis played karren similar to that on bare plaster and only pil -

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ACTA CARSOLOGICA 45/2 – 2016 189 LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN ... CONTINUATION OF TEST MODELING OF SUBSOIL KARREN FORMATION e previous results have already been presented in detail (Slabe 2005, 2009); here we add new ndings acquired with new models. For the earlier experiments (Slabe 2005), a plaster block was sliced into pillars with square cross sections and sides measuring 6 cm and a height of 30 cm (Fig. 1). e pillars were placed closely side by side in a large bucket and covered with soil. Holes were drilled in the bottom of the bucket and lastly the bucket was lled with water. e water began to percolate through the soil and run out through the holes at the bottom of the bucket. e upper two thirds of the pillar walls were cor roded by tiny features, the traces of the water percolating through the sediment and its ow along the contact be tween plaster and sediment. e entire surface of the upper sections of the pil lars was nely corroded by small cups (Fig. 2) up to 2 cm in diameter, although most are smaller. ey are the con sequence of water percolating constantly through the most permeable layer of soil. e larger cups (Fig. 2), typically found in the middle sections of the pillars, display relatively smooth surfaces. On rock, of course on a much larger scale, this type of hollow is called a “subsoil scallop” (Slabe 2005). Along the ssures or other weak spots in the rock, individual deeper semicircular or channel-shaped hol lows oen occur that in time can develop into subsoil tubes (Fig. 2). Channels with diameters ranging from one to three centimeters formed on the walls of the lower sections of lars were less sharply dissected. On the walls of a small model of uncovered karren it was possible to distinguish vertical channels at the ends of ssures (lapies wells, kar renrhren) and funnel-shaped recesses at their tops with channels below them. Tuban (1911) exposed limestone and dolomite blocks to hydrochloric and nitric acid and established that their surfaces resembled those in nature, with char acteristic dierences, of course, between the limestone and dolomite. Mowat (1962) used plates of various shapes to conrm the ndings of Lange (1959) that during the dissolving process concave areas become rounded and convex areas are sharpened. Trudgill (1985) described the smoothing of rock surfaces due to their exposure to acidic water. He proved his ndings with laboratory tests using acids and scanning rock surface with an electron microscope. Mathematical and computer modeling opens up new possibilities (Perne & Gabrovek 2009). Slabe (2009) researched rock relief of karren. Figs. 1, 2: Pillars of plaster stone forest.

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ACTA CARSOLOGICA 45/2 – 2016 190 the columns (Fig. 2 B) e locally saturated zone, which developed because the quantity of water owing along the contact was greater than the quantity that could ow out of the perforated bottom of the bucket, reached as far as the upper level of the channels. is border is oen marked by notches. On the lower surfaces of the pillars, even those cut in half horizontally, there are distinct networks of abovesediment anastomoses (Fig. 2). e angularity and square cross sections of the pil lars were preserved throughout their entire height. e characteristically pointed shape of the upper sections of the pillars is the consequence of the dispersed percola tion of water through the soil that covered the plaster. In the latest experiment, larger plaster pillars (the largest was 20 cm long and 16 cm wide, smaller ones 12 cm long and 8 cm wide; all were 30 cm in height; Fig. 3) were covered with a ner ne-grained clay less permeable for water. us the contact between the clay and the rock was also less permeable. Subsoil shas were the rst to form between the pillars. As parts of the shas, vertical subsoil channels with funnel-like mouths at their tops (Fig. 3 A) formed on the upper sections of the pillar walls. e di ameter of these features reached 3 cm. Along the less per meable contact between the plaster and the clay the water seeks the most permeable routes and merges together in ows. is was conrmed by bubbles on the surface of the water that revealed a number of distinct ponors. A special type of channel such as described in the experiment above formed on the lower section of the pillars in the locally saturated zone. Anastomoses formed on the lower surface of the pillars (Fig. 4a). e tops of the pillars gradually sharpened and ap proached the shape of a point (Fig. 4b). e process was frequently interrupted in order to examine all the phases in the development of subsoil karren. W hen the experiment ended aer 800 hours, the two larger pillars were 20 cm tall, the wider being 10 cm long and the narrower 5 cm. All that remained of the smaller pillars were two 5 cm tall and up to 1.5 cm wide pieces of plaster. Fig. 3: Development of subsoil tooth on plaster of Paris. Fig. 4: a. relief of subsoil tooth on plaster, b. shaping of plaster teeth under the soil. T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ

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ACTA CARSOLOGICA 45/2 – 2016 191 e pillars are completely pointed, which of course is most visible in the larger two pillars, especially the widest (Figs. 3, 4a, 4b). e sharp side edges were pre served. e rock relief gradually began to resemble that in the rst experiment, particularly on individual surfaces. e surface of the pillars, however, tends to be smoother as a rule. New characteristics are preserved, specically the dissection by more or less vertical and, due to the varying permeability of the contact between the plas ter and clay, more or less meandering subsoil channels (Figs. 3, 4a). Higher on the pillar walls than in the rst experiments there are horizontal or variously inclined wall notches reecting the more complete lling of s sures and the tighter contact between plaster and clay and consequently the lower permeability of the model (Figs. 3, 4a). In many places the surface of the plaster was weathered, indicating that the soluble material had not been simultaneously removed everywhere. e experiments conrm the knowledge acquired in the eld (Slabe & Liu 2009). Of course, it is necessary to consider the fact that plaster dissolves rapidly and its surface is consequently more nely dissected. W ater per colates downward through soil and various ne-grained sediments and ows through ssured rock. e peaks of rock become sharper, points or blades begin to take shape, and ssures grow into cracks. W ater then lls them with sediment beside which forms characteristic subsoil rock relief. Along the permeable contact between rock and sediment, water creeps over the entire surface enabling the formation of subsoil scallops. Along less permeable contacts, however, water consolidates to nd paths, carving subsoil shas and channels. e surface between them can become weathered. A unique rock re lief forms in locally saturated zones. e subsoil karren in the lower parts of the Dolenjska karst in Slovenia that periodically are completely ooded by groundwater are a typical example (Knez et al. 2004). MODELING OF PLASTER BLOCKS UNDER AN ARTIFICIAL RAINFALL OF DIFFERENT TEMPERATURE INNITIAL STAGES OF RAIN FLUTES DEVELOPMENT In order to clarify the formation processes of rain utes (rillenkarren), a laboratory experiment was carried out (Hada 2008, 2010). Two blocks made from plaster of Par is having a 45 inclined surface with an area of 120 mm long by 80 mm wide were placed under a vertical spray for 1,000 hours. e temperatures of tap water sprayed were 45 5 C and 24 3 C. e changing form of the rain utes was measured using photographs. e width (W , mm) and depth (D, mm) were measured from the top of the 45 inclined surface at the 1 cm, 2.5 cm, 4 cm, 6 cm, 8 cm, and 10 cm lower points on the surface every 50 hours. In both 45 5 C and 24 3 C water temperatures, the rain utes lengths (Figs. 5, 6) increased downward from the top of the 45 slopes in accordance with the time. At the same time, the widths became greater and depths became deeper (Figs. 7, 8). It is evident that the cross-sections of the rain utes at the top of the sloped surface became larger than their initial form (Fig. 9), and the widths and depths of the rain utes in the lower part were larger than in the upper part. e original sloped surface was eroded and the changes to the rain utes forms were observed. Rain utes lengths in the case of 45 5 C water temperature became longer and grew more rapidly downwards than under the 24 3 C water temperature conditions. In the case of 45 5 C water temperature, utes widths ex panded rapidly from the start up to 100 hours, and their cross-sections acquired a deep shape from the start up to 200 hours (Figs. 7, 8). In case of 24 3 C water temper ature, widths expanded slowly from the start up to 350 hours and then the depths of rain utes increased rap idly up to 550 hours when they became stable (Figs. 7,8). Finally, the volume of plaster removed from each block was estimated and compared using the rain utes pro les. e amount removed was signicantly larger under 45 5 C conditions. LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN ...

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ACTA CARSOLOGICA 45/2 – 2016 192 Fig. 6: Distribution of rain utes on plaster blocks. T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ Fig. 5: Development of rain utes on plaster of Paris blocks.

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ACTA CARSOLOGICA 45/2 – 2016 193 Fig. 9: Cross-sectional proles of plaster blocks. LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN ... Fig. 7: Relationship between width of rain utes and elapsed time. Fig. 8: Relationship between depth of rain utes and elapsed time.

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ACTA CARSOLOGICA 45/2 – 2016 194 W e rst immersed an 85 cm long plaster tube that was wider in the center in a water current (Slabe 1995a). Ma ture networks of scallops formed on the walls of the nar rower inow and outow sections while pockets formed in the wider inner section. In the sections of rapid change in the size of vortex diameters, the swirling was particu larly distinct. e pockets were found throughout the circumference. e hydraulic conditions in the tube are clearly reected on its circumference. For comparison, as a rule oblong and open scallops formed on plaster blocks immersed in a water current (Slabe 1995b). In the next experiment we drilled a 12 mm tube in a plaster block and immersed it in the water current. In 12 hours a funnel-like mouth formed at the inow side, and aer 48 hours the diameter of the entire length of the tube was evenly increased to 35 mm. A mature net work of 1.5 cm long scallops formed throughout the cir cumference (Fig. 10). Scallops also formed around the inow mouth indicating the draining of water (Fig. 11a, b, c, d). e scallops are up to 2 cm long, relatively nar row, and open and oen linked in streamlines. A sharp entrance edge gradually occurred at the mouth and al most lost its funnel-like shape (Fig. 11c). Pockets started to form behind the edge in the tube and also in places in front of it (Fig. 11d), which indicates a characteristic swirl zone, which is also typical of the changes in the size of the diameters of cave passages. Aer four days, a wide (12 cm diameter) and shallow mouth started to develop from the scallops at the beginning of the tube (Fig. 11e). Small tubes also started to form at the contact between two dierent plasters (Fig. 11a, b, c, d). ey are cracklike and branched out as dictated by the contact. e largest have circular cross sections. e more extensive tubes are found in rapidly soluble plaster. In the wider sections, there are large scallops on the circumference, 2 cm and more in size (Fig. 11c, d, e). e dissection of the system of tubes mainly fosters a variety of swirl and hy draulic conditions that dictate the development of pock ets on the circumference. A system of tubes also formed at the contact with the wooden frame that surrounded the model. In the next experiment we immersed a 73 cm long plaster tube (Fig. 12) into a water current owing at 361 l/s. e narrower inow section of the tube was 17 cm in length and 10 cm in diameter, the outow section was 21 cm in length and 5 cm in diameter, and the diameter of the outow itself was only 2.5 cm. e diameter of the middle section of the tube was 20 cm. e tube itself was 8 cm thick. ere was a ssure around the circumference of the tube. e tube was le in the water for 55 hours. It was removed several times to check the development of its formation with a special mirror. Aer 16 hours, scallops were clearly visible on the circumference in the narrower sections of the tube (Fig. 12) and there were shallow pockets at the mouths. e latter also formed on the circumference of the inow and outow sections of the tube. Fig. 10: T ube in plaster of Paris. T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ MODELING OF PLASTER TUBES W ITH A W ATER CURRENT

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ACTA CARSOLOGICA 45/2 – 2016 195 Fig. 12: Plaster tube (60 cm long) with relief. LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN ... Fig. 11: Development of tube in plaster and at the contact of dif ferent plasters.

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ACTA CARSOLOGICA 45/2 – 2016 196 e rock relief in the plaster tube reveals the conditions at the termination of the experiment. e diameter of all the sections of the tube had increased on average by 1 cm. Plaster dissolves rapidly and the rock relief changes or adapts to the conditions accordingly. e experiment was terminated when the water widened the ssure in the mid dle section and began to leak through it substantially. In the wider inow section of the tube, the scallops are 2 cm long (Figs. 12, 13a, b) and in the outow sec tion, 4 cm (Figs. 12, 13c). ese are mature networks of scallops and the scallops are therefore evenly intertwined in the network. e rst network (Fig. 13b) still displays a slight elongation of the scallops and openness on the outow side (Slabe 1995a) but the second network prac tically neither. e distribution of the rst network is more distinctly dictated by obstacles or weak spots in the plaster while the second network is also aected by space since the water swirls evenly throughout the entire cross section, meaning that the swirling action dominates the characteristics of the rock (Slabe 1995b). e walls of the wider section of the plaster tube also display scallop-like forms, particularly individual cups with wedge-shaped runo tails that indicate the local direction of the water current in this part of the tube. ey are oriented toward the widest part of the crack and also lead in that direc tion from the wall before the narrowing of the tube at the outow end of the model. ree types of ceiling pockets can be identied. e rst type forms on the circumference of the middle sec tion of the model. ey reach 1 cm in diameter and have a relatively regular semi-circular shape (Fig. 14a, b) while oblong features form only along the most distinct obsta cles (non-homogeneous elements, cracks) in the plaster. ese features are somewhat larger. Shallow pockets have runo tails in the direction of the water current. ey are a transitional form between scallops and pockets. eir formation and shape is fostered by the emphasized swirl ing along weak spots in the plaster. e second type of pocket is linked to the areas of the most distinct swirling near abrupt changes in the di ameter of the tube, specically on the walls aer the wid ening and before the narrowing of the tube. Although most of them are smaller, they can reach 2 cm in diame ter and are semi-circular or oblong in shape. ese pock ets dominate at the junction of the wall of the widest part of the model and the cross walls aer the narrowing and before the widening of the tube. Two circular depres sions up to 2 cm deep formed at these contacts whose walls were dissected by ceiling pockets that as a rule were elongated in the direction of the depression’s axis. Some pockets were intertwined. e largest and most unique pockets formed along the ssure that crossed the center of the model (Fig. 14a, b). ey are meandering and cylindrical in shape or resemble slightly narrowing cones with truncat ed tops. e mouths of the largest pockets reach 3 cm in diameter. Along the most distinct part of the ssure they lie side by side, merging in a sponge-like perforation of the plaster with a dominant inside to outside direction. Depending on the width and depth of the ssure, such areas could be 10 cm long and 7 cm wide. In one spot the water had already removed the plaster, resulting in the formation of an 18 cm long and 7 cm wide crack wid ened in the middle. e sides of the model were enclosed by wood that somewhat blocked the ow of water from the crack. e scallops found at this contact clearly show the direction of the water draining from the crack. ere are pockets reaching 4 cm in diameter on the circumfer ence of the crack. Pockets and dissected cracks formed over the entire circumference of the tube, including on the oor of the passage as well as on the walls and the ceiling. ROCK RELIEF IN THE PLASTER TUBE Fig. 13: a small scallops, b. detail of small scallops, c. larger scallops. T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ

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ACTA CARSOLOGICA 45/2 – 2016 197 MANNER AND DIRECTION OF W ATER FLO W IN A PLASTER TUBE e rock relief reects the nal hydraulic situation in the plaster tube. Of course, it is reasonable to conclude that at the beginning of the experiment the water current was faster in the outow section of the tube and that the scal lops on the circumference were smaller and the opposite applied in the inow section. Detailed monitoring was not possible. Later when the crack along the ssure wid ened, the water current owed faster through the inow part of the tube and the crack, and the current owed more slowly through the outow pipe. is is evident from the rock forms in the photographs. Fig. 14: a. ceiling pocked along ssure, b. small ceiling pockets and scallops. LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN ... e formation of deep pockets (Fig. 14a, b) along the crack, however, is by far the most telling part of the experiment. Initially, the pockets were narrow and several cm deep but along the more distinct section of the ssure they grew into domes with pockets on both their tops and their circumferences. is development is characteristic of numerous karst caves. In the model the pockets are found on the entire cross section of the circumference and are wider of course along the more permeable sections of the ssure. e rock relief and the development of the tubes clearly indicate the importance of increased pressure and the widening of the passage along weak spots. Characteristic features form with deep

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ACTA CARSOLOGICA 45/2 – 2016 198 PURPOSE OF EXPERIMENT AND DESCRIPTION OF MODEL e purpose of the experiment forcing water to percolate between layers of plaster and siporex of varying solubility was to simulate the percolation of water and the forma tion of relief in natural conditions along bedding planes of homogeneous rock with uniform granulation, along bedding planes of clastic rock containing clasts that dis solve more slowly than the surrounding material, and along bedding planes of rock with a low percentage of soluble carbonate. e two bottom layers of the stack were siporex (au toclaved aerated concrete) plates used in construction. T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ domes and pockets. Here we should especially emphasize the comparison with hypogenic caves and advise against hasty explanations that describe the majority of the em phasized forms from longitudinal cross sections of pas sages as traces of the hypogenic development of caves. e water current swirls over the entire cross section and thus pockets form. e descriptions of pockets in karst caves in most cases present ceiling pockets. ey form on the ceilings because water currents typically transport solid material that carves the oor of the passage through erosion or covers it with sediment thus protecting it from corrosion. e origin of pockets whose formation is pos sibly also inuenced by gases in the water and convec tion due to variations in their level of saturation in the solution is a subject for a future experiment. DISSOLUTION AND FORMATION OF RELIEF ALONG BEDDING PLANES OF PLASTER AND SIPOREX LA YERS e bottom layer of the two was cracked in the direction of the ow to allow water to enter the material more eas ily. e middle two layers were composed of pure plaster. e top two layers were composed of two dierent mate rials: broken fragments of plaster (with average volumes of a few cm 3 ) containing Portland cement added during the mixing for greater hardness (slower solubility) were covered with pure plaster. e lower of the top two layers held plaster fragments containing 5 % Portland cement, and the upper layer, fragments containing 10 % Portland cement (Fig. 15, Tab. 1). Each layer in the stack was 50 centimeters square and 7.5 centimeters thick. T ab. 1: Complexometric titration analysis of materials used in the experiment. Composition of layer: 1plaster, 2-plaster with 5 % Port land cement fragments, 3-plaster with 10 % Portland cement fragments, 4-siporex. Rock sample CaO (%) MgO (%) Calcite (%) Dolomite (%) Total carbonate (%) CaO/MgO Insoluble residue (%) 1 10.82 1.61 15.31 7.38 22.69 6.71 84.69 2 15.87 1.05 25.72 4.79 30.52 15.14 74.28 3 20.97 1.29 34.23 5.90 40.13 16.26 65.77 4 16.20 0.17 28.50 0.74 29.26 95.29 70.74 Fig. 15: Stack with siporex and plaster layers: e bottom two layers are siporex, the middle two layers are pure plaster, the next layer up is plaster with added fragments containing 5 % Portland cement, and the top plaster layer contains added fragments con taining 10 % Portland cement.

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ACTA CARSOLOGICA 45/2 – 2016 199 LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN ... Fig. 16: Development of forms on pure plaster layers (right) and plaster layers with harder fragments (le). Each layer was 50 centime ters square.

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ACTA CARSOLOGICA 45/2 – 2016 200 e stack of plaster and siporex layers was placed in a ume with a rectangular 1.4 x 3.4 meter cross-section. e average level of the water in the ume was 95 cm with an average discharge of 360 l/s of the water tempera ture was 12.4 C. e model was rst disassembled aer three hours. It was evident that the water had begun to intensive ly dissolve the bedding planes of the upper four layers while the siporex layers showed no changes. e surfaces of layers containing the more slowly dissolving plaster fragments clearly display mostly one millimeter wide channels that run between the harder plaster fragments. e amount (thickness) of material dissolved is clearly evident along the fragments raised in the relief. It was not possible to identify such dier ences in the layers made of pure plaster. e slowly dis solving fragments in these layers had a major impact on the erosion of the plaster. On the upstream side of the harder fragments, the plaster was removed more deeply, as it was also at the outer edges and corners of the harder fragments where the velocity of the ow was higher. e channels in the plaster between the harder fragments meander distinctly and the ow of the water has changed direction by up to 90 (Fig. 16a). e entire surfaces of the pure plaster layers start ed to show the formation of predominantly parallel bedding-plane channels a few millimeters wide ori ented in the general direction of the water ow in the ume. Plaster contains a small percentage of impuri ties comprising harder and more slowly soluble grains. Below them, relative to the direction of the ow, chan nels of even diameter change their morphology. Before the “obstacle” they widen distinctly, and below it they continue in several narrower channels (Fig. 16b). e “obstacles,” tiny harder particles, are gradually carried away by the water. e sickle-like notches perpendicu lar to the water ow seen on the surface most probably develop due to larger harder particles and transform into scallops. No dierences were observed in the dissolving of the harder fragments in either bed. Tiny channels were visible on the surfaces of the harder fragments. In most cases, the diameter of these channels was narrower than that of the channels in the pure plaster and the direction was mostly parallel to the water ow in the ume. Six hours aer the start of the experiment, the dis solving process was observed on the upstream face of the stack of plaster layers. On the upstream faces of the pure plaster layers, networks of scallops up to several mm long formed to the le and right in the direction of the water ow, and in the middle of the faces one-millimeter wide and deep cups formed. On the top two layers with the less soluble imbedded fragments, the faces of both layers had places where the water had already reached the harder fragments and the plaster between the frag ments had dissolved considerably deeper. e water owed mainly to the le and right of the model with only a small amount owing through the ne channels Fig. 17: Channels and pockets in plaster layers with harder frag ments. T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ THE COURSE OF THE E X PERIMENT

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ACTA CARSOLOGICA 45/2 – 2016 201 (bedding-plane anastomoses) between the layers, and the direction of the water ow is indicated by the scal lops. On the upstream side, the edges have already lost their sharpness, and a major invasion of water between the beds and faster dissolution was expected in the fol lowing stages. No changes were observed on the siporex layers. e channels that had already formed on the sur faces of the layers containing more slowly soluble frag ments of plaster started to deepen (Fig. 16c). In the areas where the harder fragments were close together, the ow of water went around them and picked up speed and the channels were deeper, wider, and meandering. On the surfaces of the layers made of pure plaster, predominantly parallel bedding-plane channels up to a few centimeters wide continued to form in the general direction of the water ow in the ume. e majority of the discharge between two layers owed down the middle section, while a part wedged out at the edges (Fig. 16d). e model was again disassembled aer twelve hours to observe the dissolving process. e dissolving followed the initial channels observed earlier. On the upstream faces of the pure plaster layers, scallops continued to develop to the le and right in the direction of the water ow. e faces of the upper two layers containing harder fragments were both dissolved to a great extent around the exposed fragments. W hen the model was disassembled, it was estab lished that the water had carved a central stream in the middle section of the upper layer with the harder frag ments in the direction of the water ow in the ume and had cut through the entire thickness of the layer. e larger stream of water channeled to the areas where the harder, less soluble fragments of plaster were packed to gether more densely, and where there was less cement between the fragments. e layer began to disintegrate. Simultaneously, due to its faster ow between the layers, in some places the water also started to carve beddingplane channels into the harder fragments of reinforced plaster as well as into the pure plaster. Consistently, the streams no longer avoided the harder fragments as they had at the beginning of the experiment (Fig. 16e). e channels became wider and deeper. e traces of swirling water and more rapid dissolving continued at the con tacts between the harder fragments and the pure plaster and where there were clusters of harder fragments. In pure plaster, the great majority of the beddingplane channels developed over the entire length of the layers; the ow of water between two layers increased its speed, the channels became larger and wider. Only two areas about one square decimeter in size on the le and right side of the layers remained undissolved (Fig. 16f). In front of the still undissolved patches, the water swirled and carved pockets a few centimeters in diameter and up to 1 cm deep upstream and downstream. W hile the wa ter entered the entire width of the model in a more or less evenly thick layer, due most probably to the merging of streams between the still undissolved and adjoined parts of the two layers, the water created mostly evenly deep bedding-plane channels at the outow side of the model. Fig. 18: e turbulent ow of water on pure plaster layers re shaped parallel channels into cups and a network of scallops. LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN ...

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ACTA CARSOLOGICA 45/2 – 2016 202 T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ No changes were observed on siporex layers. e model was next disassembled aer 24 hours. Even though each plaster layer had dissolved in overall thickness by around 20 % (on the top and bottom of the layers in the direction of the water ow), the model still maintained its original shape. e layer containing plas ter fragments reinforced with 10 % Portland cement had dissolved less. A bedding-plane pocket had started to form in the lower of the two siporex layers, and a slight dissolving was noticeable in the area of the crack in the upper siporex layer. e extensive dissolving of the plaster in the top most layer with harder fragments continued. In the low er layer with harder fragments, the meandering beddingplane channels generally oriented in the direction of the water ow in the ume and which had also formed on the harder fragments deepened (Fig. 16g). Larger pock ets of irregular shapes formed due to the swirling of the water mostly upstream of the harder, less soluble plaster fragments (Fig. 17). In several places, pockets up to a few cm deep formed in the plaster on the bottom side of the layer. W here the water entered the model, numerous deeper and shallower bedding-plane channels formed. Due to swirling, the water carved 2 cm deep and 2 to 3 cm wide pockets on both layers that merged into chan nels. Shallower channels also formed alongside the in soluble parts of the plaster. A chaotic network of somewhat irregularly shaped scallops began to develop to the le and right in the di rection of the water ow along the insoluble part. Similar forms occurred at the contact of the layers of pure plaster, but the channels, pockets, and scallops are about 100 % deeper on the upper surface of the lower layer than on the bottom of the upper layer (Fig. 16h). W hen the model was inspected aer 48 hours, the dissolving of both top and bottom surfaces had made the layers about 50 % thinner. Further minor dissolving was also evident along the crack in the upper siporex layer. A signicant change was observed on the surfaces of the pure plaster layers. To the le and right of the undissolved section of plaster, the water transformed the more or less parallel channels into numerous pock ets and a mostly irregular network of scallops due to its completely unhindered ow through the model and strong turbulence (Fig. 18). A similar development of channels into a network of pockets and scallops due to the largely unobstructed ow of water between two layers was also observed on the inner surfaces between the two layers made of pure plaster (Fig. 16i). Parallel channels transformed into an irregular network of very long and narrow scallops were only preserved in the middle section of these layers. In the top layer with harder plaster fragments, the water widened the already-carved channel that divided into two legs with a 40 angle by around 50 % (Fig. 16j). e stream created a new discharge channel and tore a number of the harder plaster fragments from the model at the split section of the entry channel and from several discharge channels and carried them away. e stronger and more turbulent ow deepened the pockets in the plaster, dissolved the contact areas between the harder plaster fragments and plaster even faster, and in most cases rounded the originally sharp edges of the harder fragments. Aer 72 hours, the water had almost entirely dis solved the plaster layers. e harder plaster fragments were almost all that was le of the layers containing them (Fig. 16k). e upper of the two layers made of pure plaster was almost completely dissolved, while the siporex layers remained almost unchanged. e water carved a channel along the crack in the upper siporex layer. Only one layer made of pure plaster remained al most whole, although thinned to around 2 cm. All of the original mostly parallel channels had been transformed into a network of pockets and scallops (Fig. 16l). RESULTS AND DISCUSSION Plaster models reveal the subsoil shaping of rock and the development of its subsoil rock relief below soil of diverse composition with consequently variously perme able contact and in locally saturated areas of the contact (Figs. 3, 4). Subsoil scallops form over the entire surface when water creeps downward along a permeable contact while subsoil shas and channels form along less perme able contacts. Longitudinal notches indicate the prevail ing levels of groundwater while anastomoses occur along horizontal contacts. e original sloped plaster surface was eroded and the changes of rillenkarren forms were observed (Figs. 5, 6). Rain utes lengths in the case of water tem perature, 45 5 C become longer and faster downwards than water temperature, 24 3 C. In the case of water temperature, 45 5 C, widths expanded rapidly from

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ACTA CARSOLOGICA 45/2 – 2016 203 LABORATOR Y MODELING OF KARST PHENOMENA AND THEIR ROCK RELIEF ON PLASTER, SUBSOIL KARREN, RAIN ... the beginning time to 100 hours, cross-sections have deep shape from the beginning time to 200 hours. In case of water temperature 24 3 C widths expanded from the beginning time to 350 hours and depths of rain utes increased rapidly from start to 550 hours. e rock relief of a plaster tube cave clearly shows its development under dierent hydraulic conditions. Pock ets are found on the entire circumference where larger vortexes form in the water current. Due to the higher wa ter pressure in a tube passage, the water creates distinct notches along areas of weakness in the rock, primarily along ssures and bedding planes where deep domes with pockets form. is is a frequent characteristic in sections of plaster caves with a large inow and limited outow of water, although in natural caves, pockets are mostly found on the upper parts of the rock circumfer ence because the oor can be further shaped by material carried or deposited as sediment by the water (Figs. 12, 13, 14). Dierent networks of scallops are the trace of the characteristics of the rock on which they form and the hydraulic conditions, the velocity of the water current, and the impact of the space on the swirling of the water. e third model experiment revealed the dissolving and formation of relief on the surface of layers of vary ing solubility and composition. At the beginning of the experiment, the water dissolved only the faces and outer contacts between the layers. e next stage, with a pre dominantly laminar and slower ow between layers, saw the formation of longitudinal and meandering anasto mosis channels, in some places the origins of a network of scallops, and along the harder, more slowly dissolving fragments, the beginnings of pockets and domes created by swirling water. In the last phase of the experiment, due to the faster and more turbulent ow and swirling along the harder fragments, the water completely trans formed the longitudinal and parallel channels into a deep network of pockets, domes, and scallops. Smaller chan nels developed into larger spaces, and the even swirling of water in the newly formed larger spaces fostered the formation of a network of scallops. Toward the end of the experiment, the scallops started to grow, indicating a gradual slowing of the water ow through the model. W ith the slow water ow, the small bedding-plane anas tomoses grew into a larger channel with wall forms char acteristic of a slow water ow. e authors acknowledge the nancial support from the Slovenian Research Agency (research core founding P60119-0618). REFERENCES Allen, J.R.L., 1972: e origin of cave utes and scallops by enlargement of inhomogeneities.Rassegna spe leologica Italiana, 14, 1, 3. Curl, R.L., 1966: Scallops and utes.e Transactions of Cave Research Group of GB, 7, 2, 121. Dzulynski, S., Gil, E. & J. Rudnicki, 1988: Experiments on klukarren and related lapis forms.Z. Geo morph. N. F., 32, 1. Ewers, R.O., 1966: Bedding plane anastomoses and their relation to cavern passages.Bulletin of the national Speleological Society, 28, 3, 133. CONCLUSION is type of laboratory modeling has once again proved to be demonstrative and useful for studying karst surfaces and caves. It enables us to deepen our knowledge about the manner of karst formation and its development. It is worth to continue. ACKNO WLEDGEMENT

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ACTA CARSOLOGICA 45/2 – 2016 204 Ewers, R.O., 1972: A model for the development of sub surface drainage routes along bedding planes .M. Sc. esis. University of Cincinnati, pp. 84. Ewers, R.O., 1982: Cavern Development in the Dimen sions of Length and B readth .PhD thesis. McMaster University, Hamilton, pp. 398. Gins, A., 2009: Karreneld landscapes and karren land forms.In: Gins, A., Knez, M., Slabe, T. & W . Drey brodt (eds.) Karst rock features – karren sculpturing . ZRC Publishing, pp. 13, Ljubljana. Glew, J.R. & D.C. Ford, 1980: A simulation study of the development of rillenkarren.Earth Surface Pro cesses, 5, 25. Goodchild, J.G. & D.C. Ford, 1971: Analysis of scallop patterns by simulation under controlled condition.e Journal of Geology, 79, 1, 52. Hada, A., 2008: Formation Processes of Rillenkarren on the Surface of Plaster Block (in Japanese with Eng lish Abstract).Transactions – Japanese Geomor phological Union, 29, 3, 301. Hada, A., 2010: Eects of Temperature on Formative Processes of Rillenkarren on the Surfaces of Plaster Blocks (in Japanese with English Abstract).Japa nese Geomorphological Union, 31, 1, 1. Knez, M., Slabe, T. & S. ebela, 2004: Karst uncovered during Bi – Korenitka motorway construction (Dolenjska, Slovenia).Acta Carsologica, 33, 2, 75. Lange, A., 1959: Introductory notes on the changing geometry of caves structures.-Cave studies, 1, 69. Lauritzen, S.E., 1981: Simulation of rock pendants – Small scale experiments on plaster models.In: Beck, B.F. (ed.) Eight international congress of spele ology . Georgia Southwestern College, Americus, pp. 407, Georgia. Mowat, G.D., 1962: Progressive changes of shapes by so lution in laboratory.Cave notes, 4/6, 45. Quinif, Y ., 1973: Contribution a l’etude morpholoq ique des coupoles.Annales de speleologie, 28, 4, 565. Perne, M. & F. Gabrovek, 2009: e problems of rillen karren development: a modeling Perspective.In: Gins, A., Knez, M., Slabe, T. & W . Dreybrodt (eds.) Karst rock features – karren sculpturing . ZRC Pub lishing, pp. 55, Ljubljana. Pluhar, A. & D.C. Ford, 1970: Dolomite karren of the Niagara Escarpment, Ontario, Canada.Zeitschri Fr Geomorphologie 14, 4, 392. Rudnicki, J., 1960: Experimental work on utes develop ment.Speleologia, 2, 1, 17. Slabe, T., 1995a: Cave Rocky Relief and its Speleogenetical Signicance .Zbirka ZRC, 10, ZRC Publishing, pp. 128, Ljubljana. Slabe, T., 1995b: Experimental modelling of cave rocky relief forms in Paris plaster.Atti e Memorie della Commissione Grotte E. Boegan, 32, 65. Slabe, T., 2005: Two experimental modelings of karst rock relief in plaster: subcutaneous rock teeth and rock peaks exposed to rain.Z. Geomorph. N. F., 49, 107. Slabe, T., 2009: Karren simulation with plaster models.In: Gins, A., Knez, M., Slabe, T. & W . Dreybrodt (eds.) Karst rock features – karren sculpturing . ZRC Publishing, pp. 47, Ljubljana. Slabe, T. & H. Liu, 2009: Signicant subsoil rock forms.In: Gins, A., Knez, M., Slabe, T. & W . Dreybrodt (eds.) Karst rock features – karren sculpturing . ZRC Publishing, pp. 123, Ljubljana. Trudgil, S., 1985: Limestone geomorphology .Longman, pp. 196, London. Tuban, F., 1911: Die Oberchenformen bei Carbonat gesteinen in Karstgegenden.Centr. F. Min. Geol. und Paleont., 1911, 343. T ADEJ S LABE, A SAMI H ADA & MARTIN KNEZ


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