Karst Processes Research Articles

Copper-Bearing Mineralisation in the Upper Devonian Limestones: A Case Study from the Historical Teresa Adit in the Świętokrzyskie Mountains, Poland

The studied copper ore deposit is located in Miedzianka Mountain (Świętokrzyskie Mountains, central Poland). This deposit was exploited from the 13th century to the 1950s; therefore numerous historical adits are currently present. One of these is Teresa adit (established in 1805), consisting of underground mining corridors and natural cave developed in the Upper Devonian limestones, partially transformed by mining works. Samples of copper- and rock-forming minerals in limestones collected at seven sites within the richest copper-bearing mineralisation in this adit were studied with petrographic investigation of thin sections, micro-area chemical analysis (EDS), and XRD. This study shows the presence of various minerals: (a) Cu-Fe sulphides (relics of chalcopyrite) and Cu sulphides (covellite, chalcocite), (b) Cu-Fe oxides (cuprite and hematite), (c) Ca and Cu carbonates (calcite, azurite, and malachite), (d) clay minerals (Fe-Mg illite), and (e) micro-crystalline silica (quartz). For the first time in the studied deposit, we described chalcopyrite relics in cuprite pseudomorphosis, hematite with admixture of vanadium in pinkish-creme veins in limestones, and the presence of an admixture of Fe-Mg illite and microcystaline silica within cracks of limestones. In addition, for the first time, unit cell parameters of malachite and azurite from Miedzianka Mountain were determined, indicating very low substitutions of atoms other than Cu in their structures. We suppose that the minerals studied were formed during three types of copper mineralisation processes: (a) hydrothermal (relics of chalcopyrite), (b) secondary weathering (chalcocite, covellite, cuprite, hematite), and (c) adsorptive mineralisation (azurite, malachite). The latter stage is related to residuum, which consists of a mixture of Fe-Mg illite and micro-crystalline quartz, which was formed during the dissolution of limestones in karst processes in some crevices. We proposed a model of the formation of copper carbonates in the adsorption stage of the copper-bearing mineralisation in Miedzianka Mountain deposits. Two generations of calcite veins (older—red calcite and younger—crème-pinkish calcite) were also detected. Mineralogical–petrographical studies of samples revealed a high scientific and educational value. Due to the fact that the Teresa adit is planned to be made available to geotourists, this work is worth presenting to the public either in the adit and/or in a local museum in Miedzianka village.

Karstified zone interpretation using deep learning algorithms: Convolutional neural networks applications and model interpretability with explainable AI

Ground penetrating radar (GPR) is a non-invasive geophysical method that can be used to assist in mapping karstified zones in outcrop analogous for the characterization and understanding of carbonate oil reservoirs. Supported by GPR data, it is possible to understand the behavior of karstification processes in carbonate rocks and thus expand the knowledge to the reservoir level. In addition, Machine Learning (ML) and Deep Learning (DL) algorithms have allowed the application of computer vision techniques to identify geological structures and facies based on geophysical data, but mostly focused on seismic data, while GPR based applications still need to be explored. In this context, this study seeks to apply deep learning models in synthetic as well as real GPR data and attributes (similarity, energy, instantaneous frequency, instantaneous phase and Hilbert trace/similarity) based on convolutional neural networks using the U-Net architecture capable of assisting in the mapping of karstified zones imaged through GPR surveys. Moreover, explainable artificial intelligence (XAI) techniques using SHapley Additive exPlanation (SHAP) values are applied to improve the interpretability and explainability of the generated models. These techniques were employed in order to assess the rules found by the models, the modeling quality and the presence of biases in the model. The SHAP values show that the energy attribute was the feature that provided more information in both synthetic and real models. Instantaneous frequency and similarity were the second and third most important features in the synthetic model, while the other attributes presented less relevant contributions. Finally, we generated a model capable of aiding in mapping karstified zones using GPR data and attributes, promoting the understanding of complex models and allowing greater cooperation between experts in the geosciences and results generated through deep learning techniques.

Burial stylolites enhance karst dissolution and control cave geometry in heterolithic carbonates, Salitre Formation, Brazil

Understanding the karstification process in fractured carbonates is a key factor in developing and exploiting fractured and karstified reservoirs. This study documents the relationship among the 2D geometry, stratigraphy and petrophysical properties of a cave system developed in a Neoproterozoic mixed carbonate-siliciclastic sequence. We applied a multidisciplinary and multiscale approach that combined structural geological surveys, cave imaging by Laser Detecting and Ranging (LiDAR), linear scanlines, stratigraphic logs, uniaxial compressive strength (UCS), mercury-intrusion porosimetry, and 2D image analysis. We found that bedding-parallel stylolites in dolomitic limestone consist of mm-to cm-thick high-porosity zones (up to 20% measured via 2D image analysis). They acted as fluid conduits that enhanced bedding-parallel dissolution. Field and thin section analyses showed that beds with close spacing and thicker stylolites are more karstified and dissolved than beds showing greater spacing or completely devoid of stylolites, indicating that stylolitic zones act as flow pathways in low porosity-permeability carbonates. Primary porosity, pore size distribution, density and capillary pressure of host rocks have no direct relationship with karstification intensity. We conclude that clusters of burial stylolites may control the hypogenic cave geometry. These findings have direct implications for subsurface permeability prediction in karstified carbonate reservoirs.

A New Species of the Genus Niphargus Schiödte, 1849 (Crustacea: Amphipoda: Niphargidae) from Groundwater Habitats of the Tarkhankut Upland, Crimean Peninsula

A new species of the genus Niphargus Schiödte, 1849 (Crustacea: Amphipoda), co-occurring with water louse Asellus cf. aquaticus (Linnaeus, 1758) (Crustacea: Isopoda) in deep wells, is described from the Tarkhankut Upland, located in the northwestern part of the Crimean Peninsula. Niphargus tarkhankuticus sp. nov. corresponds to a separate phylogenetic lineage (the “tarkhankuticus” ingroup), also including several undescribed species from the coastal habitats of the Black Sea (the Crimean Peninsula, the southern Caucasus and the northern coast of Turkey), which is related to the paraphyletic European “stygius-longicaudatus” group. The divergence of the “tarkhankuticus” ingroup from the related European species probably appeared in the Late Miocene age, about 11–10 Mya, related to the separation of the Eastern Paratethys for different basins (Euxinian, Alpine and Pannopian). At the same time, the speciation within the ingroup started in Pliocene, about 5.76–3.6 Mya, and correlated with the Black Sea leveling and the drainage of coastal marine carbonate accumulations, including the Tarkhankut Upland. Intraspecific values of COI mtDNA gene markers (p-distances) for N. tarkhankuticus sp. nov. are about 2%, showing that the division into a number of isolated subpopulations, probably associated with local tectonic movements, the active formation of the river network, and further karst processes in the Tarkhankut Upland occurred during the Pleistocene (since 2.58 Mya). Analysis of stable isotopes (δ13C/δ15N) revealed that only discovered macrocrustaceans in the studied wells of the Tarkhankut Upland have non-overlapping trophic niches, with A. cf. aquaticus possibly feeding on algae/periphyton, while the trophic position of N. tarkhankuticus sp. nov. is close to predators.

Landscapes of the Formoso river watershed, Mato Grosso do Sul - Brazil

The present research aims to identify, classify and map the landscape units of the Formoso River Watershed, located in the state of Mato Grosso do Sul - Brazil. The classification is based on geological, hypsometric, slope, horizontal dissection, vertical dissection, and erosive potential energy data of the relief. In addition to soil and land use data, as well as several theoretical and cartographic references that deal with the karst and non-karst environment. The study identifies seven first-order landscape units and 23 s-order units. The distinction between karst and terrigenous (non-karst) systems stands out in the units, and different features are observed in the landscape. In Serra da Bodoquena and in the areas of poljes, the landscapes result from the karst process on rocks. In the residual hills, on the flat surfaces and in the alluvial plains, the landscapes present their genesis associated with rocks of terrigenous origin. The duality highlights the uniqueness of the area. The study presents the complexity and heterogeneity of the landscape, and aims to contribute and expand the studies of karst environments, promoting preservationist and conservationist actions, as well as public policies in areas with similar characteristics in the State of Mato Grosso do Sul.

Base-level poljes in the Sivas gypsum karst, Türkiye

The Sivas Basin, Central Anatolia, includes one of the most outstanding gypsum karst terrains in the world, covering an area of 2140 km2. The karst landscapes are developed on late Eocene gypsum deposits. The fact that the polje shapes that are commonly seen in the limestone karst terrain also seen in the Sivas gypsum karst area further increases the importance of this area in terms of geomorphology. This study is focused on the explanation of the morphometric properties and formation mechanism of poljes around the Kızılırmak River in the Sivas gypsum karst area. The geomorphological evolution of the Sivas gypsum karst area was controlled by the Kızılırmak River drainage system formed in the Early Pliocene. Polygonal doline karst is common on the High Karst Plateau (or erosional-denudational surface) formed during this evolution process, while subsidence dolines, hanging valleys, and poljes are common on the Low Karst Plateau. A total of 14 poljes, most of which are drained underground, and a corrosion plain were identified around the Kızılırmak River in the Low Karst Plateau. The boundaries of some of the poljes, the area of the largest of which is 6.3 km2, and hence their strike is controlled by faults. These poljes are base-level poljes, which bases are approximately at the river level and developed in the water table fluctuation zone. In addition to the structural lines in the formation of the poljes, the beginning of a blind valley-like karstification process, especially in the lower parts of the hanging valleys, mostly as a result of the collapse doline formation (showing the estevalle feature), changes in the water table level in the epiphreatic zone, and in addition to the precipitation, the aggressive river floodwaters that invaded the polje floor were effective. Due to the rapid dissolution of gypsum, the development of polje must have been affected by the incision and deposition periods of the river. The Tödürge Lake depression most probably has been shaped by collapse dolines.

Potential Caves: Inventory of Subsurface Access Points on the Surface of Titan

AbstractWe propose that cycling hydrocarbon rains on Saturn's moon Titan are likely to create subsurface conduits through dissolution geology of the extensive organic and largely‐soluble substrate. In this work we inventory different terrains and locations on Titan that could host potential subsurface access points or caves. Using Cassini data, we identified and enumerated a cryovolcanic construct, filled and empty lake basins that may have formed through karstic processes, estimates of closed valleys in organic plateaux, and enigmatic equatorial pits. Our preliminary survey identified over 21,000 estimated locations for future exploration to identify potential caves and cave forming processes on that world. We speculate that the exploration of these caves could teach us about the cave forming processes, as well as the past climate history and perhaps even chemical deposition history on Titan.

Relationship between Karstification and Tectonism in the Upper Jurassic Evaporite Formation: A Case Study of the Lalla Fatna Escarpment Safi, Morocco

The Upper Jurassic Evaporite Formation accumulated up to 200 m of interbedded gypsum-carbonates layers across the coastal cliffed region of Safi (Morocco) have been affected by karstification process, resulting in karst collapse and subsidence structures associated with faulting, fracturing and different types of instabilities, which are among the main causes of natural hazard risk, impacting the socio-economic and environmental issues. Surface investigation (physiognomic approach) allowed the characterization and identification of deep-seated and subjacent gypsum interstratal stages and showed that the karstic features are controlled by orientations of faults and fractures. To highlight the relationship between tectonics and karstification, in this area, fracture orientations were studied, and the result of analysis of diagrams showed that, in most cases, orientations of karst landforms are controlled by regional tectonic features.

Potential Geotourism Attractions on Nusa Penida Island, Klungkung Regency, Bali

Nusa Penida Island is one of the leading tourist destinations in Bali Province. Tourist destinations on the Island consist of various types of beaches, hills, caves to unique landscapes formed due to the karstification process. Nusa Penida Island is geologically composed of limestones (the Selatan Formation) with various types such as clastic limestones and coral limestones(Hadiwidjojo et al, 1998). In addition to the unique geology of Nusa Penida Island, it also has archaeological uniqueness. The Gede Cave shows that Nusa Penida was once inhabited by prehistoric humans (Abdillah, 2011). During the COVID-19 pandemic, tourism seems to be forced to accelerate and requires new tourist attraction innovations that support sustainable tourism. This research discusses geotourism-based tourist attractions that can be developed and explored in Nusa Penida. The approach used is geological diversity inventory method (Geological Agency, 2017). Primary data was obtained through survey activities. From the research carried out, it can be concluded that 10 geological site locations in the Nusa Penida area have the potential to be developed as areas with geotourism attractions, which offer unique geology, especially regarding karts landscape processes and one of the key geological history on the island of Bali. In addition, Nusa Penida Island has the potential to be developed as a geopark as an effort to develop sustainable tourism in Klungkung Regency.

The sediment at the end of the tunnel: Geophysical research to locate the Pleistocene entrance of Gruta da Companheira (Algarve, Southern Portugal)

AbstractUntil recently, evidence of Neanderthal cave use in the Algarve (Southern Portugal) came only from the site of Ibn Ammar. Over the last couple of years, archaeological excavations inside another cave, Gruta da Companheira, yielded Mousterian stone tools associated with possible human fossils. The discovery of this assemblage is groundbreaking because it may contribute to enlighten the Neanderthal/cave relationship and explain the dearth of similar sites in the Algarve. Gruta da Companheira, however, is a complex karst system, which was partly destroyed during its accidental discovery. As result, the original entrance of the cave remains unknown, and it is unclear how sediments, archaeological materials and Neanderthals accessed the site. To tackle these issues, we combined geomorphological observations with speleological, Electrical Resistivity Tomography (ERT) and Ground‐Penetrating Radar (GPR) prospections. Our data indicate that Gruta da Companheira was probably accessed from the hilltop through a sub‐vertical entrance. Additionally, our results suggest the existence of yet unexplored shallower cavities connected with the already known passages of Gruta da Companheira. These results will guide the opening of new excavation areas at the site. The limestone bedrock hosting Gruta da Companheira has been extensively dissolved by karst processes. Therefore, it is necessary to focus future research on the cave infillings to clarify whether Neanderthals exploited the cave's inner chambers or alternatively limited their occupations to the hilltop and geogenic processes reworked their materials into the endokarst system shortly after their stays. The deep karstification and partial collapse of the hill hosting Gruta da Companheira are common in limestone outcrops that occur throughout the Western Algarve. Poor visibility and poor accessibility of this karst area, densely covered with shrubby vegetation, are factors that need to be considered when addressing the scarcity of Middle Palaeolithic cave sites in this region.

Soil erosion rates on sloping cropland fragment underlain by contrasting lithologies

This study examines the pattern of soil erosion rates in a cropland fragment underlain by limestone and purple sandstone (referred to as the CLP) in the Three Gorges Reservoir Region (TGRR) using the 137Cs and 210Pbex techniques. A total of 96 bulk cores and 18 sectioned cores were collected from the CLP. In addition, 4 bulk and 4 sectioned cores were extracted from each of two reference sites. Based on the 137Cs and 210Pbex inventories obtained from these cores, the soil erosion rates were assessed. The results indicate that the 137Cs and 210Pbex inventories both increase downslope, while the calculated soil erosion rates both decrease. This implies that the intensity of soil erosion decreases downslope, which is a combined response to the effect of gravity, the short slope length, and the gentle gradient of the cropland. The soil erosion rates derived from 137Cs were generally higher than those determined using 210Pbex. This shows that soil erosion was more intense from 1954 onward than during the period between 1920 and 1954, reflecting the impact of disturbance by cultivation, which has increased rapidly over the past 60 years. The soil erosion rate on the limestone area was similar to that in the purple sandstone area, but higher than that reported from karst regions experiencing rocky desertification. This suggests that, providing that there is no evidence of karst rocky desertification, the soil erosion intensity in cropland underlain by limestone is similar to that underlain by purple sandstone. This result provides a new insight into the pattern of soil erosion intensity on the cultivated hillslopes of karst and non-karst regions at the scale of the cropland fragment. It will also help to improve our understanding of surface processes in karst and non-karst areas subject to intense cultivation.

Quaternary paleoenvironments based on pedogenic, sedimentary and karstic processes in the coastal geosystems of Cozumel Island, Mexico

The Quaternary carbonatic deposits of the Cozumel Island are mainly reefs and calcarenites in which karstic features, red clayey paleosols and layers of calcretes provide a record of terrestrial paleoenvironments still poorly explored. A main section, Cantera Payo, and three complementary sections: Cantera Transversal, Aerolito and Chempita were studied. Besides field work, micromorphology, physicochemical and mineralogical analyses of soils and calcretes were done. C and O stable isotope analysis was also conducted in calcretes. The cyclicity of sedimentary, karstic and pedogenetic processes was established. The chronological frame was obtained through the correlation dated calcretes and coral samples from Yucatan Peninsula, with ages ranging between ∼Marine Isotope Stage (MIS) 7 to MIS 1. Two paleo-karstic surfaces were identified, labeled as PK1 (older) and PK2 (younger). The PK1 surface showed multi-face karst features as collapse breccias, dissolution pits and pipes, and karstic pockets filled with lithified brown and red paleosols. The red paleosols exhibited abundant redoximorphic features. Clay mineralogy in paleosols and modern soil is similar, with vermiculite and minerals of the kaolinite group. We interpret they are the result of moderate weathering under a seasonal tropical climate like that of present-day conditions. PK1 is capped by a calcrete layer, whose age probably corresponds to the Marine Isotope Stage (MIS) 6 (164 a 135 ka). Therefore, the host rock and the karstification and pedogenetic processes should occur before (probable during MIS 7) The stable carbon isotope composition of this calcrete has a mean δ13C value of −10.40 ‰ that suggests the presence of a C3 plant cover. During the MIS 5, poorly cemented calcarenites accumulated in the island related to the sea level rise during this interglacial stage. This calcarenite level has less developed karstification and pedogenetic processes. Another laminar calcrete with root traces and septal alveolar structure is found on top of the studied sections formed in the MIS 5 and the transition to MIS 4. Its δ13C value ranges between −9.40 ‰ and − 10.27 ‰ also related to a C3 plant cover. In the period between MIS 4 and MIS 1, karst development and pedogenesis is observed on the island, evidenced by the formation of caves and reddish-brown soils.

The properties of faults in the Brazil pre-salt: A reservoir characterization perspective

Subsurface characterization of faults and fault systems is a central piece to describe the subsurface permeability architecture of a carbonate reservoir during field development. Data integrity and quality are often compromised due to the challenges (mud losses and stuck pipe) that are posed when drilling into a fault zone. Core is frequently not recovered or in very poor condition (rubble) that make quantitative description of a fault zone very challenging. For these reasons wellbore trajectories tend to avoid fault zones leading to a sampling bias. As a result, many authors default to using field analogs to fill in the knowledge gap in fault properties that are required to build robust subsurface reservoir models. In this work, we select a subset of wells from the pre-Salt, offshore Brazil, where faults have been either intersected by a well or investigated by a well test. We use case studies to illustrate how observations made across a multidisciplinary dataset can be brought together to provide insights into likely ranges of fault properties. We discuss subsurface observations of fault zones in the pre-Salt in the context of analogs to propose end members of fault architecture that can have an impact on reservoir performance. Results suggest that these faults act as conduits for fluid flow. Their internal structure is characterized by a high density of fractures that often show evidence of dissolution enhancement. In the case of early syndepostional structures, early karst processes are responsible for enhancing fracture porosity and leading to the development of cavernous porosity. Faults developed during burial have a lesser degree of diagenetic overprinting, resulting in an overall lower pore volume. However, permeability (and its degree of anisotropy) in both cases is several orders of magnitude greater than that of the matrix. We have used numerical forward modeling of pressure derivatives to evaluate fault permeability values that yield 10's of darcy permeability associated with such features.

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.

Литология карстовых отложений разреза верхнего визе Залесской площади (северо-западная часть Оренбургской области, Россия)

Poorly studied deposits of the Upper Visean section of the south-east of the Orenburg region are one of the promising objects of geological exploration. A powerful stratum of dolomite breccias is described in one of the wells of the Zalesovo area in the lower part of the undifferentiated the Venev, Mikhaylov and Aleksino strata of the Visean section. The section is composed of secondary dolomites with relics of primary textures and structures. Dolomitization complicates interpreting the genesis of deposits and conduct detailed sedimentological studies. Lithotypes of rocks are identified based on the analysis of a set of data from lithological and mineralogical studies. Lithotypes: 1) secondary dolomites with relics of primary textures, 2) dolomite breccia with clay-carbonate cement, 3) secondary breccia dolomites with relics of primary textures, 4) dolomite breccia. A detailed lithological description of the lithotypes is given. The features of their formation are determined. Reservoir properties of rocks are analyzed. It has been established that the sediment complex encountered in the section of the Uppen Visean section of the Zalesovo area are the result of different stages of karst formation and following transformation of rocks. Reservoir properties of rocks depend on the development of post-sedimentation transformations. Karst processes and their products require further study at the regional level and consideration when conducting geological exploration on productive reservoirs of the Uppen Visean section.

Enigmatic annular landform on a Miocene planar karst surface, Nullarbor Plain, Australia

AbstractThe Nullarbor Plain is a ~200,000 km2planar karst surface in southern Australia, underlain by Cenozoic shallow‐water limestones. During the Miocene the area was uplifted, and although the plain is generally considered extremely flat, locally, the geomorphology of the Nullarbor Plain retains evidence of earth surface processes across a long, middle Miocene‐to‐present time span. The accessibility of the recent 0.4 arc‐second TanDEM‐X digital elevation model (DEM) by the German Aerospace Centre motivated the search for other possible fine‐scale landforms that would previously have been unresolvable. The analysis of DEM images revealed an enigmatic annular landform with an outer diameter between 1200 m and 1300 m. It consists of a circular elevated rim and a central dome. Its morphology is distinct from other landforms observed on the plain, and cannot be readily explained as a part of known active or inferred/expected processes on the plain (e.g., fluvial, aeolian, karst, tectonic or extra‐terrestrial impact processes).More recent karst processes (dayas formation) overprinting the landform indicates the presence of the annular structure prior to dayas formation. A unique microbial boundstone facies sampled from the bed‐rock of the annular structure supports an interpretation of long‐lived, at least partial retention of a primary depositional structure. Differential carbonate deposition, especially bioherm growth, was a likely origin of the annular topographical expression of the present‐day landform and is comparable to biogenic structures in the modern day deeper Great Barrier Reef.

Coastal hazards mapping using high-resolution UAV image and DEM. A Case study in Siung Beach, Gunungkidul, Indonesia

The southern coast of Gunungkidul, which is adjacent to the subduction zone, is prone to various coastal hazards. The increasing number of visitors to the beach leads to more exposure and increases the risks. This study aims to determine the coastal hazards in Siung Beach, Gunungkidul, Yogyakarta. A high-resolution aerial image and DEM were acquired using a low-cost Unmanned Aerial Vehicle. The acquired images were processed using Structure from Motion (SfM) photogrammetry to generate an orthomosaic image with 5cm spatial resolution. A worst-case tsunami hazard scenario (12 m) was executed using raster filtering on the generated UAV-DEM. Based on the tsunami inundation model, most of the buildings are affected by the worst-case tsunami scenario. According to orthomosaic interpretation, rip current hazard is also spotted on the eastern part of the beach. The rip current is considered a channel rip, a stationary rip current affected by the bathymetric condition. Potential rockfall due to slope instability might be occurred on the southern part of the beach, as a former enormous mass movement can be delineated from the orthomosaic image. Siung Beach is formed by the combination of volcanic origin and karst process, resulting in undulating topography. Due to various coastal hazards in Siung beach, disaster management planning should be established to reduce the risks.

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.

Kozaklı (Nevşehir) jeotermal alanındaki obrukların jeofizik yöntemler kullanılarak belirlenmesi

In this article, the temporal and spatial development of probable sinkholes in the close vicinity of a couple of sinkholes that occurred in 2007 and 2018 in the Kozaklı (Nevşehir) geothermal field, which is one of the most important thermal tourism centers where treatment with radon gases and mud can be carried out in Central Anatolia, was investigated using the multi-electrode resistivity method and core drilling data. The primary geothermal water aquifer consists of Palaeozoic aged marbles, the secondary Eocene aged limestone aquifer and cover rocks are the impermeable units of the area. Geothermal waters gain heat by geothermal gradient, granitic intrusions, and radiogenic ways. The depths, temperatures, and pH values of the wells belonging to geothermal water resources vary between 60 and 1493 m, 45 and 96 °C, as well as 6.22 and 6.61, respectively. Two-dimensional electrical resistivity methods were used to determine the dimensions of the collapse structures. In the geophysical studies examining the depths of 15-30 meters, surface fractures around the sinkhole, a subsidence structure nearby the active highway approximately 20 meters to the east, travertine was found around the pothole, especially in the east and north of the hollow structure. This data verified with log data obtained from core drilling. These findings are indicators for the ongoing karstification process.

Identifying the Multi-Scale Influences of Climate Factors on Runoff Changes in a Typical Karst Watershed Using Wavelet Analysis

Identifying the impacts of climatic factors on runoff change has become a central topic in climate and hydrology research. This issue, however, has received minimal attention in karst watersheds worldwide. Multi-resolution analysis (MRA), continuous wavelet transform (CWT), cross wavelet transform (XWT) and wavelet transform coherence (WTC) are used to study the teleconnection in time and frequency between climate change and hydrological processes in a typical karst watershed at different time scales. The main results are: (1) All climatic factors exhibit a main cycle at 12-month time scales with runoff changes, but the main periodic bandwidth of rainfall on runoff changes is much wider than that of temperature and evaporation, indicating that rainfall is the main factor affecting runoff changes. (2) In other cycles, the impact of rainfall on runoff changes is the interlacing phenomena with positive and negative, but the impact of temperature and evaporation on runoff change is mainly negative. (3) The response of runoff to rainfall is in time in the high-energy region and the low-energy significant-correlation region and has shown a positive correlation with a smaller phase angle, but it is slightly lagged at 16-month time scales. Moreover, the runoff change lags behind temperature and evaporation for 1–2 months in those regions. (4) It has been found that there is a strong effect of rainfall over runoff, but a lesser effect of temperature and evaporation over runoff. The study sheds light on the main teleconnections between rainfall, evapotranspiration and surface runoff, which in turn might help to attain the better management of water resources in typical karst watersheds.