Underground Karst Research Articles

The effect of reservoir expansion from underground karst cave to surface reservoir on water quality in southwestern China.

Due to the excessive exploitation of traditional energy sources, the attention paid to water energy has increased in recent years. As an important means to effectively utilize water energy, reservoirs play an important role in drinking water, irrigation, flood control, and drought resistance. However, utilizing reservoirs often led to water quality issues resulting from the interaction of nutrients and hydrological conditions, especially due to the special structure of karst areas. Because of the change of hydrological conditions by the effect of dam construction, the dynamic of water quality will be more obvious in karst areas with a fast exchange of water and contaminants between underground and surface streams. In the present study, the change in water quality of a karst reservoir, the Muzhu Reservoir in the Houzhai Catchment, was studied. Long-term monitored datasets (1981-2002) and water quality datasets of more recent years were used to assess the effect on the water quality of reservoir expansion from the underground reservoir to the surface reservoir in a karst area. Long-term series datasets had shown that the hydro-chemistry type had been changed from HCO3-·SO42--Ca2+·Mg2+ type to HCO3--Ca2+ type in the short term after the reservoir's expansion. The chemical components of water originating from a rock background reduced markedly after the reservoir's expansion, whereas the content of the anthropogenic contribution in the water decreased after the expansion, except in April and May. Isotopic characteristics showed that δ15N-NO3- and δ18O-NO3- values were positively correlated before and after the reservoir expansion, but the slope of the linear regression before the expansion was 0.34, while the slope of the linear regression before the expansion was close to 0.7. This indicated that although denitrification and assimilation may occur simultaneously after the reservoir's expansion, the role of denitrification on nitrate removal decreased, which resulted in nitrate accumulation in the karst reservoir. The results highlighted that nitrate accumulation in karst reservoirs should be monitored to decrease nitrate concentration in the future.

Applying the Show Cave Assessment Model (SCAM) on cave tourism destinations in Serbia

This paper explores the current state and the perspectives of sustainable cave tourism development of show caves in Serbia. The results of the research were determined through the application of the newly developed methodology—Show Cave Assessment Model (SCAM). The obtained results of the research indicate shortcomings in terms of the protection of underground ecosystems and the tourist infrastructure. Moreover, based on the obtained data, future perspectives of the cave tourism development in Serbia include the establishment of karst parks, the affirmation of speleoarchaeology and the creation of innovative show cave routes. The focus is also placed on the importance of applying appropriate geoethical principles in cave tourism. The adventurous concept of cave tourism, which includes visiting caves that are not arranged for classic cave tours, and requires special equipment and professional guides, is particularly highlighted. Final results of the reserarch confirmed that the popularization and application of ethically responsible behavior towards underground karst ecosystems is necessary in order to preserve speleological geoheritage for current and future generations of local residents, tourists, managers, scientists and researchers, mountaineers, enthusiasts and speleologists.

Migration and transformation of soil mercury in a karst region of southwest China: Implications for groundwater contamination

Guizhou Province is located in the heart of a karst zone in southwest China, which is one of the largest karst areas in the world. Given the fragile surface ecosystem and highly developed underground karst structure, the migration and transformation of soil Hg may impact groundwater quality in karst environments with high Hg background concentrations. This study examines the vertical migration and transformation of soil mercury (Hg) in two karst catchments, Huilong and Chenqi, with the former containing high Hg contents associated with mineralization and the latter representing regional background Hg. The results show that the soil Hg pool in the Huilong catchment was as high as 44.4 ± 4.2 g m−2, whereas in the Chenqi catchment was only 0.17±0.02 g m−2. Compared with farmland soil, forest soil showed a significant loss of Hg. The results of L3 X-ray absorption near edge structure of Hg indicated that α-HgS, the primary mineral of Hg ore, gradually changed to other mineral types during soil formation. In Huilong catchment, the proportion of organic bound Hg(SR)2 out of total Hg decreased from 44.0% to 20.3% when soil depth increased from 10 cm to 160 cm in farmland soil profile and from 39.3% to 34.5% in forest soil profile, while the proportion of ionic Hg increased with soil depth, from 4.2% to 10.7% in the farmland soil profile and from 6.7% to 11.6% in the forestland soil profile. Results from the triple-mixing isotope model show that soil Hg accounts for more than 80% Hg in groundwater in the two catchments. Results from this study indicate potential risks of soil Hg entering into groundwater in this karst area.

Sources and Biogeochemical Processes of Nitrate in the Laolongdong Karst Underground River Basin, Chongqing

Samples of sewage, well water, and underground river water of the urbanized Laolongdong karst underground river basin in Chongqing, China were collected during July 2019 and October 2020 and measured to determine the nitrate origin and biogeochemical processes based on geochemistry and dual nitrate isotope (δ15N-NO3- and δ18O-NO3-) data. The results showed that:① the isotopic nitrate compositions of sewage ranged from -3.3‰ to 14.6‰ for δ15N-NO3- and from -5.2‰ to 20.6‰ for δ18O-NO3-, which indicated that nitrate originated from manure and sewage, fertilizer, and soil organic nitrogen. The δ15N-NO3- and δ18O-NO3- of well water varied from 3.1‰ to 12.6‰ and 2.9‰ to 8.9‰, respectively, suggesting nitrate was mainly from soil organic nitrogen and manure and sewage. For the underground river water, the δ15N-NO3- and δ18O-NO3- ranged from 5.6‰ to 28.6‰ and from -2.0‰ to 15.7‰, respectively, suggesting that municipal sewage and manure were the dominate nitrate sources. ② Based on the MixSIAR model, manure and sewage were the primary nitrate source of the underground river water, accounting for 89.1% of the total contribution, whereas the contributions of soil organic nitrogen, fertilizer, and atmospheric precipitation were 4.4%, 3.4%, and 3.1%, respectively. ③ In the basin, the concentration ratios of COD:ρ(NO3-) from low to high were as follows:well water (0.14-5.15), underground river water (0.50-9.36), and sewage (4.08-89.50). Only 50% of well water samples with COD:ρ(NO3-) were slightly higher than 0.65, which is the minimum stoichiometric ratio for denitrification occurrence. This indicated that there were insufficient COD concentrations to support that denitrification occurred in the well water. This was further verified by no significant enrichment of nitrogen and oxygen isotopes. As much as 90% of underground river water samples had a COD:ρ(NO3-) higher than 0.65, and the dual nitrate isotopes were simultaneously enriched with a δ15N:δ18O of 1.8, which is within the ratios ranging from 1.3 to 2.1, indicating that denitrification occurred. The COD:ρ(NO3-) for all wastewater samples was much higher than 0.65, of which 25% were higher than the stoichiometric ratio (29.34) for the occurrence of dissimilation reduction nitrate to ammonium (DNRA). The δ15N-NO3- and ρ(NH4+):ρ(NO3-) of sewage increased simultaneously, indicating that DNRA may have occurred in the sewage.

Imaging of karst cave using ground penetrating radar and electrical resistivity tomography: a case study in Shandong, China

A denudation-dissolution hilly area about 20km southeast of Jinan city, Shandong Province, China is characterized by karst features. The upper part of the area is covered by quaternary Holocene flood and slope deposits, and the lower bedrock is Ordovician limestone, which is a moderately weathered massive structure with developed joints and fissured fractures, and solution grooves can be seen locally. The local government to better serve the surrounding residents and the surrounding facilities, here is planned for the substation, for later security construction, electrical resistivity tomography (ERT) method and ground penetrating radar (GPR) method were used to investigate the underground karst caves. The aim of the joint use of the two methods is to better describe the characteristics of karst landform, a 160 MHz shielding antenna was employed in the GPR survey, while the frequency limits the scope of the depth of the electromagnetic waves can reach. However, it provides a lot of shallow stratigraphic information, which well represents the boundary between overburden and bedrock and the development of karst. The use of ERT method further makes up for the depth defects of the GPR method, and two-dimensional imaging of underground resistivity distribution was carried out, which also helps to further identify the characteristics of underground karst. The combination of the two geophysical methods can accurately delineate the development of underground karst, which also proves that the combination of the GPR method and ERT method has good application value in karst landform detection, and can also be applied to a similar geological survey.

Investigation and characterization of karst landform with GPR: a case study in Shandong, China

A substation is an important infrastructure for city operation and people’s life. The proposed site, 37 km northeast of Zaozhuang, Shandong province, is located on top of Cambrian limestone, most of which is directly exposed or covered by thinner Quaternary silty clay. The Karst processes on the surface contribute to the dissolution of gullies and limestone fissures in the surface topography. Directly the evidence shows that the study area is karst cave or the possibility of larger crack, the potential risk impact on subsequent substation the safety of the pile foundation installation construction. Thus led to the ground penetrating radar (GPR) investigation on the bedrock of karst development. The aim of this study was to characterize the development of karst caves in the shallow surface and delineate their locations. The 80 MHz shielding antenna was used to study and characterization of the karst features. The results of GPR method show that the application of a low-frequency antenna can satisfy a certain detection depth and well characterize the development of underground karst, which also proves that GPR method is very practical in the detection of karst landform and can be applied to identify similar geomorphic features.

Characteristic of Lang Son Karst Poljes in Vietnam and Geohazards

In the karst regions of Vietnam, there are many different terrains. The most important one is karst polje. Because there are a lot of residential areas and important economic regions. Based on the study of Geomorphology, geological structure analysis, Geophysics document analysis, and karstification process research at Lang Son karst polje. The author gives conclusions: Lang Son karst polje was formed from the limestone of Bac Son Formation, 700 – 800 m thick. Lang Son karst polje was formed from anticline structure, the limestone of Bac Son Formation that has high karstification level. Lang Son karst polje has only one karst aquifer which is a water supply source for residential areas in Lang Son city. This karst aquifer distributes in limestone blocks of the Bac Son Formation. Geohazards on Lang Son karst polje include collapse, sinkhole, flood, and pollution of water. Among them, the most dangerous one is the collapse of the underground karst caves.

Scientific assessment of negative changes in the state of karst groundwater

Centralized water supply in remote settlements is often difficult or impossible, so there is a need to use a non-centralized water supply. The article develops a method for an expert assessment of the negative change in the state of underground karst waters based on a paired analysis of complex indicators of the protection of the aquifer. To assess the vulnerability of non-centralized water supply sources, five factors are used, including the geological structure of the territory, the level of surface and underground runoff, the development of the karst network, precipitation regime electrical conductivity, and mineralization of groundwater. The test was performed using the method of inversely weighted distances (IDW). The vulnerability assessment of karst waters was carried out in the area of 10 key control points identified during the deployment of the hydrogeological control system in 2017. Based on various geological and hydrological indicators, the discrepancy between the vulnerability assessment of karst waters was no more than 15 %. The conditions under which it is advisable to use direct measurements or geoelectric methods to monitor karst groundwater's state are identified.

Karst morphologies and ghostrock karstification

Underground karst morphologies are often used by scientists to speculate on the conditions of formation of karst cavities, for example: flow in vadose or phreatic zone, flow on sedimentary filling and fluvial flow. However, recent development of the ghostrock karstification models provides new insights on the origin of these morphologies. For ghostrock karstification, the chemical dissolution of calcite is coming along with the drainage of the soluble species while the undissolved particles remain unremoved. On the other side, karstification by total removal, undissolved particles are simultaneously eroded from the system leading to the creation of a macroscopic void. This paper presents numerous field observations of karst morphologies, which were previously considered as resulting of karstification by total removal, in ghostrock karstification context. From them, it has been demonstrated that most karst morphologies may result from both processes, which requires great caution in the interpretation of these microforms.

Bihourly Subterranean Temperature and Relative Humidity Data from the Nullarbor Plain, Australia (Nov 2019–Mar 2021)

This research provides bihourly temperature and relative humidity data from ten measuring locations in eight caves from one of the largest contiguous arid karst areas in the world, the Nullarbor Plain in south Australia. The current data span the period from November 2019 to March 2021, and represent the first continuous published monitoring of the subterranean features in this area. The data were recorded using ten TGP-4500 Tinytag Plus 2 self-contained temperature (resolution ±0.01 °C or better with a reading range from −25 °C to +85 °C) and relative humidity (resolution ±3.0% or better with a reading range from 0% to 100%) data loggers and are available in the form of a spreadsheet. The text also describes reported (but only occasional) visits to the caves, so that the data for those particular days and/or hours can be treated as anthropogenically influenced. The data have great potential to provide insight into underground karst processes, air mass movements, hydrogeology, speleothems and (palaeo)climate, current climatic changes, and biology.

Vulnerability Assessment of Karst Underground Waters in the Territory of Non-Centralized Water Supply

This paper considers an individual approach to assessing the vulnerability of karst groundwater. It is based on the allocation of such indicators as the geological structure of the observed territory, the concentration of runoff entering the karst channels, and the precipitation regime. Due to regional climatic, hydrogeological and landscape features, a private methodology for assessing the vulnerability of karst groundwater has been developed. To assess the vulnerability of sources of non-centralized water supply, a factor is taken into account, including such indicators as lithology, soil thickness, and the presence of a karst base. The most intense karst processes occur on river terraces, valley slopes. For this purpose, a factor is taken into account, including the level of river flow by hydrogeological posts, underground flow, karst craters, tectonic faults, and vegetation. The development of karst is also promoted by high gradients of the underground flow and underground water outlets in riverbeds and coastal slopes. For this purpose, the factor is taken into account, which is formed on the basis of the criterion of the development of the karst network and the hydrographic network.A relatively large amount of precipitation, especially in the form of rain, and low evaporation determine the increased values of surface and underground runoff and, accordingly, the development of dissolution and leaching processes. Among the external factors, the solubility of minerals is significantly affected by the total mineralization and chemical composition of the dissolving waters. As a result of the observations, spatio-temporal dependencies were identified in the controlled territory.

Emerging Ecotone and Microbial Community of a Sulfidic Spring in the Reka River near Škocjanske Jame, Slovenia

During long periods with no precipitation, a sulfidic spring (Smrdljivec) appears in the dry bed of the Reka River before sinking into the karst underground. The study characterizes the area’s geological setting, development of microbial communities and an ecotone, and impact on the vulnerable karst ecosystem. Geological mapping of the area, stable isotopic analyses, field measurements, and physico-chemical and toxicity analyses were applied to elucidate the environmental conditions. The spring’s microbial diversity was assessed using cultivation methods, microscopy, and metagenomics. Sulfur compounds in the spring probably originate from coal layers in the vicinity. Metagenomic analyses revealed 175 distinct operational taxonomic units in spring water and biofilms. Proteobacteria predominated in developed biofilms, and a “core” microbiome was represented by methylotrophs, including Methylobacter, Methylomonas, and Methylotenera. Diatoms represented an important component of biofilm biomass. A combination of environmental factors and climatic conditions allows the formation and accessibility of emerging biodiversity hotspots and ecotones. Details of their dynamic nature, global impact, and distribution should be highlighted further and given more protection.

SOME ASPECTS OF POLISH-UKRAINIAN GEOLOGICAL AND GEOMORPHOLOGICAL RESEARCHES OF WESTERN VOLYN-PODILLIA DURING THE POLISH INVASION

The proposed article is based on an analysis of publications on field observations published in the then Polish and Ukrainian periodicals, collections of materials from scientific forums at various levels, works collections of individual Polish and foreign scientific institutes, etc. The purpose of the article was an attempt to analyze and generalize the research results of the study area in the field of Quaternary geology and geomorphology. It should also be noted that publications from the listed sections of physical geography are encountered quite sporadically and in significantly smaller numbers than articles on purely geological disciplines such as mineralogy, petrography, lithology, tectonics, etc. The study of geological and geomorphological objects and processes was carried out on the territory of Western Volyn-Podillia, which at that time was a part of the Polish-Lithuanian Commonwealth. The works mainly concerned the study of the stratigraphy of anthropogenic sediments distributed in the Podillia loess and loess soils, continental glaciations and related glacial and fluvial-glacial deposits, surface and underground karst, etc. It was established that significant in volume and depth of generalization of works on the geological and geomorphological structure the region features at that time was not. The studies that were carried out were not systematic, they were often carried out on the researchers initiative and without adequate funding, with localization mainly in the territory with open at that time deposits of certain minerals types. Analysis of publications can be stated as follows: the study of Quaternary deposits of the region and loess in particular was carried out with extensive use of laboratory studies, paleontological method, chemical, particle size distribution mineralogical and petrographic analyzes, the method of separation of loess minerals in heavy liquids, paleontological and archaeological observations, etc., were progressive at that time. It should be noted that individual reports on the determination of the age of the Quaternary strata were poorly synchronized with each other and a reliable generally accepted scale for the division of these deposits in this period was not agreed. During this period, factually substantiated schemes of geomorphological zoning of both the Podillia region as a whole and its individual components were proposed. Regular relationships of the relief features of the region with the lithogenic base, neotectonic movements, glacial and fluvial-glacial processes are traced. Significant progress is noted in the study of stratigraphy, lithology of local loess strata, problematic issues of their genesis are discussed. Among the few works on the study of the loess cover of Volyn-Podillia, the work of Yu. Polianskyi and Yu. Tokarskyi attracts attention first of all. The works on the study of loess are important due to: a) their almost ubiquitous distribution in the described territories; b) value for stratigraphic subdivision of the Pleistocene; c) controversial genesis; d) widespread use for the production of bricks and tiles. Work on the study of surface and underground forms of the Podillia karst has spread. Systematic mapping of individual underground cavities begins which gave impetus to their use in the future as objects of tourism. The largest number of works is devoted to the problems of studying the relief and modern physical and geographical processes in the interwar period. At the same time, along with purely descriptive publications, works appear where conclusions are based on the use of cartographic materials, which allowed researchers to identify significant patterns in the morphological features of the region. In the period under study, numerous publications by soil scientists also appeared, in which Quaternary sediments are considered as parent rocks on which soils were formed, the dependence of the type of soil on the lithology of the underlying rocks is established.
 In general, the works of Polish and Ukrainian researchers in the characterized period laid a reliable foundation for modern ideas about the geological and geomorphological features of the region.
 Keywords: geomorphological studies, Quaternary deposits, glacial deposits, stratigraphy, morphology, loess deposits.

Investigation on pollution sources of a Karst Underground River in southwest Guizhou

by means of karst hydrogeology investigation, pollution source investigation, water pollution status investigation, water quality sampling and detection, The water pollution of large karst underground river in Muerdong of southwest Guizhou Province was investigated and demonstrated. The analysis shows that:(1) the catchment area of groundwater unit in Muerdong-qingping River is about 270 km2, and there are many karst pipelines in the area, and finally discharge at the exit of the underground river at the lowest discharge datum level in the area. (2)there are mainly four replenishment subsystems in the underground river, it is found that the karst water system of Dajiang and Tanping river is finally discharged through the Q4, Q5 and Q6 karst springs or the underground river of Muerdong River, and neither the spring water nor the underground river is polluted, the outcrops of Yangjiaba Karst water system and Bayan karst water system in Muerdong underground river are Q1, Q2 And K35. The spring water and groundwater in the cave are polluted (3) the main pollution of the underground river of Muerdong is from the excrement of livestock and poultry in DK farm in the karst water system of yangjiaba, which is discharged into the underground pipeline of the underground karst river through the falling water cave. The water source area of Muerdong underground river is located in the strong karst area, the geological environment is fragile, and the suitability of developing large-scale aquaculture industry is poor. The government needs to enhance the understanding and use for reference in attracting investment.

Source, Partition and Ecological Risk of Polycyclic Aromatic Hydrocarbons in Karst Underground River Environment, Southern China

As the main source of drinking water in the karst areas of southern China, underground rivers play an important supporting role in local economic and social development. However, due to the special aquifer structure in the karst areas of southern China, polycyclic aromatic hydrocarbons (PAHs) can easily enter the water environment of underground rivers and cause serious pollution, which will affect the water quality safety. In this study, Qing-shui Spring underground river in Nanning city was selected as a representative of the typical underground river in southern China, and the pollution characteristics, source analysis, ecological risk assessment and diffusion law of PAHs were studied. The results showed that the total concentration of PAHs in groundwater and surface sediments was in the range of 282.42–464.88 ng/L and 400.14–1194.69 ng/g, respectively, and the overall concentrations of PAHs were below the moderate pollution level. Pollutant discharge and physical and chemical properties of PAHs caused the concentrations of PAHs to decrease gradually from upstream to downstream, but the proportion of high-cyclic PAHs increased gradually. According to the source analysis results of the ratio method, PAHs sources in groundwater were mainly biomass combustion sources in the upstream, oil sources in the middle and mixed sources in the downstream. Sediment and groundwater had some differences. The middle and upper reaches were the source of biomass combustion, while the middle and lower reaches were the mixed source. The ecological risk assessment results showed that the ecological risk of groundwater was at a moderate level, while the ecological risk of sediment was at a low level. Benzo[a]anthracene (BaA) and benzo[b]fluoranthene (BbF) in groundwater and acenaphthylene (Acy) and fluoranthene (Flu) in sediment should be monitored intensively. Appropriate control measures should be put in place to prevent further pollution. Partition coefficients varied from 0.73 to 3.85 L/g in the sediment–water interface, increasing with the rise of PAH compounds. All of the organic carbon partition coefficients (Koc) in the sediment–water interface were higher than predicate values based on the typical model of equilibrium distribution; this indicated that PAHs were strongly adsorbed in the sediment. The linear free energy relationship coefficient between the Koc value and the n-octanol-water partition coefficient (Kow) was 0.85 but the slope was lower than 1, indicating that sediment in the Qing-shui Spring underground river had weak lipophilic characteristics and adsorption ability for PAHs. The results can provide a reference for the risk assessment and pollution control of PAHs in the karst underground rivers in South China.

A Cave Occupied by Cave Bears for Thousands of Years in the Sobrarbe-Pirineos UNESCO Global Geopark (Huesca, Aragon, Spain)

The Sobrarbe-Pirineos UNESCO Global Geopark shows an extremely well-developed underground karst relief as a result of the great abundance and thickness of its limestone formations. The most important Pleistocene vertebrate site within the Geopark is Coro Tracito Cave at Tella. The fossil association is made up exclusively of bones belonging to Ursus spelaeus from the upper Pleistocene, accumulated over several thousand years. Based on scientific analysis of the fossil bones, an interesting public outreach project has been organized, involving the refurbishment of the site within the cave and the creation of a permanent exhibition called the Tella Cave Bear Museum. These two infrastructures are visited by thousands of tourists each year and constitute the main geoscientific tourist attraction of the Sobrarbe-Pirineos Geopark.

The Omniscient Spring – the Whispering Water: Man and potajnica

Potajnice (intermittent/rhythmic springs) are a rare hydrographic phenomenon exclusively present in karst areas. They appear as a result of the rising and emptying of the siphon in the underground karst reservoir, while the phases when the water flows over and drains down most frequently last for several minutes or several hours. They are often accompanied by a distinct noise (rumbling, sizzling, bursting) which adds to the mysteriousness of this phenomenon. Up to this point in time, around one hundred of these flows have been detected worldwide and, when it comes to Europe, they are most frequent in the Balkan Peninsula, primarily in the range of the Dinarides. The subject of this paper is the human perception of this unusual hydrological phenomenon and reaction to it, which has brought about the birth of many interesting ceremonies and beliefs. In areas with predominantly Orthodox and Islamic traditions, the water from these springs is often regarded as healing and miraculous, which is not the case in the northwestern areas closer to Central Europe. Nevertheless, the entire area is eager to provide a logical explanation for this phenomenon. In the more distant past, some of these places had been subject to Christianisation through construction of churches in their vicinity and provision of a Christian interpretation of local beliefs and tales. Man interpreted the functioning of these flows in two ways – either as the existence of a supernatural being in the underground canal, which occasionally presents a barrier to the water flow, or as activities of a higher power which infallibly judges the moral righteousness of human beings and thereupon decides to either let the water flow or stops its flow. The ancient human tendency to tame the supernatural has enticed man to look for a way to predict the flow intervals which, under certain circumstances, could ensure or confirm social power for an individual or group. At some point, the monks took over the perennial monitoring of the flow rhythm of one such source in order to harmonise their prayers for the appearance of the “healingˮ water. The relation between man and the potajnica has always been ambivalent; therefore, one river, which for centuries was called Sveto vrelo (the Holy Spring), also has an alternative name – Đavolje vrelo (the Devil's Spring). Also, men tend to cross significant distances to reach water from one spring, but avoid drinking water from others precisely due to the identical disappearance of the flow. Nevertheless, these springs represent unrivalled points where the richness of the spirit and tradition of the population visiting them is embedded, and, more generally, the relationship between man, as the human being, and this enigmatic force of nature.

Tectonic Structure and Relationship with Sinkhole Harzard in Bang Lung Area, Cho Don District, Bac Kan Province

By integration of remote sensing images analysis, geology, geomorphology, hydrogeology, geophysical method, and drilling data, the paper illustrates the structure tectonics, causes, and initial mechanism of a sinkhole forming in Bang Lung, Cho Don, Bac Kan province. The NE-SW normal slip faults are an essential fault system in the area, which created Bang Lung graben valley. This fault system also forms large fracture zones, creating advantage conditions for the groundwater runoff both vertically and horizontally to eroded and dissolved carbonate rock-forming underground karst caves. These are favorable natural conditions for forming a sinkhole. The sinkhole hazard in the Bang Lung area is initiated by some main factors such as tectonic activity, thickness, and characteristics of unconsolidated sediment layers, groundwater fluctuation, karst caves, and human activities. The most human impacts are mining exploitation and agricultural cultivation that promote sinkholes occurring faster and earlier. The horizontal and vertical movement of groundwater dragged the material on the ceiling karst caves into ground spaces. Thereby, weakening the cohesion of the unconsolidated sediment above caves leads to gravitational unbalance and creates a sinkhole. This study has also shown potential sinkhole areas in Bang Lung, which helps the authorities and local people in sinkhole prevention and mitigation mission.

Study on land subsidence law of shield tunnel overlying karst

In the process of tunnel construction, underground karst is one of the main causes of ground collapse accidents. Using the GTS/NX finite element software, the numerical analysis of karst with different shapes and locations is carried out, and the law of surface subsidence caused by the karst overlay on the tunnel is obtained, which provides the basis for the deformation of the stratum where the karst cave is located, the prediction of accident, the risk assessment and the formulation of the treatment scheme.

Land cover and land use change in karst region Devetashko plateau

The Corine Land Cover (CLC) is a digital data about land cover which is distributed into 44 classes whereas for the territory of Bulgaria the CLC classes are 36. The minimal mapping unit is 25 hectares (for 2D objects and 100 m for linear objects). Data sets for the years 1990, 2000, 2006, 2012, and 2018 are available, as well as for the changes which have occurred between each couple of years (1990–2000, 2000–2006, 2006–2012, and 2012–2018). The great data sets provide to track over a nearly 30-year period of land cover changes in model karst regions which are strongly vulnerable to anthropogenic and natural influences. This paper considers the changes in the land cover types on the Devetashko plateau – a typical karst plateau in North Bulgaria. Land cover and land use changes affect directly the processes of modern karst-genesis, the soil-vegetation cover, the quantity and quality of underground karst waters.