Oksana Anatolievna Mazaeva

The sulphate–carbonate karst in the southern part of the Bratsk Reservoir has been active throughout the reservoir’s operation. Long-term monitoring of the coastal zone, interpretation of multi-temporal images, and field studies at the Khadakhan key site resulted in the creation of a conceptual model of coastal geosystem functioning in areas of sulphate–carbonate rock development under conditions of long-term and seasonal fluctuations in the reservoir water level. The structure of interactions within the coastal geosystem is organized at three hierarchical levels: (1) the intra-rock level, (2) the level of interacting factors, and (3) the level of interacting exogenous geological processes, whose activation is driven by an external factor—changes in the reservoir’s water level. We identified five stages of gully formation and the cyclic nature of the karst–erosion process in the coastal geosystem under conditions of seasonal and long-term reservoir water-level fluctuations. Our findings indicate that, when regulating reservoir water levels, dramatic drawdowns should be avoided. This conceptual model aims to improve the understanding of the impact of large reservoir operation on the dynamics of a complex of interacting coastal processes, as well as on the peculiarities of karst development in a boreal climate.

This paper presents the results of a comprehensive study of a catastrophic karst-suffosion sinkhole that occurred on September 19, 2024, in the Khadakhan-Melkhituy karst massif (Southern Angara region) and resulted in a human fatality. Using UAV‑derived data, the morphometric parameters of the sinkhole were determined (depth 9.7 m, volume 412 m³), and a comparison was made with historical monitoring data from the 1980s. Laboratory tests performed on samples collected from the sinkhole walls revealed that the 9.7‑m thick cover sequence consists of structurally unstable loess‑like loams and sandy loams, with anomalously high silt content (up to 84 %) and porosity (up to 64 %). The interaction between karst and suffosion processes plays a key role in the sinkhole formation. The long‑term (57‑year) backwater effect of the Bratsk Reservoir and its cyclic level fluctuations caused leaching of sulfate‑carbonate rocks, promoting mechanical removal of silt‑sized particles from the cover sequence by percolating water. A two-stage mechanism of karst-suffosion sinkhole development was identified: from the formation of a loosening zone above an ancient karst cavity to the instantaneous (brittle) roof collapse triggered by a technogenic factor – the weight of heavy agricultural machinery. The study of the reactivation of karst‑suffosion processes in the backwater zone of the Bratsk Reservoir contributes to the understanding of modern geodynamic processes and ground surface deformation mechanisms, including those induced by technogenesis.

The article presents an innovative methodology for applying Semantic Web technologies to support fundamental geological research. The problem of semantic i

The article presents an innovative methodology for applying Semantic Web technologies to support fundamental geological research. The problem of semantic integration of heterogeneous geological data, characterized by different scales and interdisciplinarity, is considered. A five-stage methodology is developed, including domain analysis, ontological conceptual modeling, data transformation into a knowledge graph, deployment of a distributed data access infrastructure based on the conceptual model, and integration with processing and analysis procedures. Practical testing was conducted on three case studies: analysis of geochemical data for assessing territory pollution levels, creation of an information system about faults, and research on reservoir shoreline dynamics. The proposed ontological approach ensures compliance with FAIR principles and overcoming the "semantic barrier" in geological research. It is shown that Semantic Web technologies enable a transition from fragmented information arrays to a holistic semantic space of geological knowledge, opening new opportunities for generating comprehensive scientific hypotheses and cross-disciplinary research.

The study area is located in the Ulaanbaatar basin and is characterized by complicated environmental conditions determined by the peculiarities of an extremely continental climate with high rainfall intensity, a structural–tectonic pattern, the geological structure of the Ulaanbaatar intermountain depression, high seismic activity reaching 8 points, and the occurrence of catastrophic flash floods. In the conditions of rapid urban expansion, the high population density and housing development of Ulaanbaatar, and the implementation of large investment projects, it is an urgent task to assess the exogeodynamic hazard of the Ulaanbaatar catchment basin and develop the concept of geoecological safety of the territory. These methods and approaches consist of combining a complex of methods of engineering geology and geomorphology: monitoring the dynamics of exogenous processes; environmental assessment; the analysis of development factors (climatic, geomorphologic, tectonic, and lithological) and interaction of processes; laboratory methods of analyzing the composition, structure, and properties of soils; a detailed morphometric analysis of catchment areas; and the application of the basin approach. Based on the analysis of topographic maps on a scale of 1 : 50 000 and of digital relief models in GIS programs, the parameters of the drainage network of the catchment areas and of energy and basin geometry were calculated and reflected on map layers, and specialized maps were compiled. A detailed assessment of erosion-prone soils (composition, structure, and specific properties) revealed a moderate resistance of sediments to geodynamic impacts. As a result, maps of flood hazard of catchments under different rainfalls—short intensive heavy rainfalls and long-term rains—were compiled. The elaborated concept of geoecological safety of territories includes successive stages of works aimed at (a) identifying the exogeodynamic hazard, (b) the organization and implementation of monitoring works, (c) assessing geoecological safety with respect to hazardous exogenous geological processes, and (d) the development of recommendations for further use and specification of information.

The shores of the Bratsk reservoir are widely affected by bank gullies. We monitored the short- and medium-term gully dynamics at three key sites. The interaction of karst-erosional, aeolian-erosional, and gully and shore erosion processes were determined and presented as conceptual models. Gully and shore erosion were the dominating processes in the Rassvet site in the period of heavy rainfall and the maximum shore edge retreat at high water level stand (2009–2010). During 2011–2013 aeolian process prevailed over erosion due to small rainfall and low water-level stand, and aeolian material accumulated in the gullies. A high water-level period at the Ulei site resulted in shore edge retreat, hanging of gully mouths, formation of wave-cut holes in the shore scarp, and rejuvenation of retrogressive erosion in gully thalwegs. The combined action of karst and gully erosion processes led to a maximum increment in gully size (4486.34 m³), recorded at the Khadakhan site in 2004–2008 (at periods of reservoir water-level lowering following water saturation of shore massif at high water levels). This case study shows that the dynamics of the processes, their interactions, and environmental changes are characterized by a certain cyclicity corresponding to water-level changes.

The activation of linear erosion forms in the south of the Irkutsk amphitheatre was stimulated by the construction and exploitation of the Bratsk water-storage reservoir in mid-XX century. In the paper, the characteristics and interaction of natural and technogenic factors influencing the erosion process are described. The construction of reservoir gave rise to new erosion mechanisms such as karst-erosion, aeolianerosion and abrasion-erosion, which did not occur under the natural (undisturbed) conditions. The large-scale topographic maps were used for evaluation of the spatial distribution of erosion in the shore zone; the active erosion processes were observed in 16 areas of the Bratsk reservoir's shore zone; the overall erosionaffected area of the Bratsk reservoir's shore is 332.9 thousand m2.

В пределах береговой зоны острова Ольхон выделены три генетических типа берега: структурно-абразионный, абразионный и аккумулятивный, которые подразделены на подтипы в соответствии с развивающимися экзогенными геологическими процессами: абразионно-оползневой, абразионно-обвальный, абразионно-осыпной, абразионно-эоловый и биогенный. Общая протяженность берегов острова Ольхон с учетом прибрежных озер составляет 225 км, из которых 153 км (68%) составляют абразионные берега; 57 км (25,3%) – структурно-абразионные; 15 км (6,7%) – аккумулятивные.