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The authors discuss applicability of phase characteristics of surface waves in monitoring of underground openings and tunnels. The mathematical model of surface wave propagation along extended cavities is presented. The properties of the numerical solutions obtained using the model are analyzed, including the amplitude and frequency characteristics, and the phase and group velocities of the waves. It is possible to recover elastic properties of a medium using the dispersion curves of the phase velocities. The data of numerical modeling of surface wave propagation along cavities of different geometry using the method of finite spectral elements are presented. The calculated results of the axisymmetrical and three-dimensional problems of surface wave propagation along cavities are studied.

Bischofite rock samples from a well at the Vologda underground gas storage are subjected to rheological tests. The time curves of deformation are plotted at different axial and lateral stresses. A viscoelastic phenomenological model is proposed, and the equation to describe these dependences is obtained. Being developed and algorithmically implemented, the experimental data interpretation procedure allows determining rheological characteristics of test rocks at different stress ratios. It is found that rheological properties of bischofite weakly depend on depth.

The study is made of the changes in climatic characteristics, such as air temperature, atmospheric pressure and precipitation and their relationship with the large-scale atmospheric circulation over Siberia for the climatically significant time interval 1979-2018. The study area was limited to 50-70° N and 60-110° E. In calculating the series of territory-averaged values of surface temperature, atmospheric pressure and average precipitation, daily observational data from NOAA-GSOD were used. The characteristics of baric formations of cyclones and anticyclones were determined on the basis of surface synoptic maps for standard meteorological periods. It was found that by the end of the study period the trend in surface temperature and precipitation is positive, and the trend in atmospheric pressure is negative. The trend in characteristics of baric formations, such as the number of cyclones and anticyclones, is positive, as is the pressure trend in the centers of anticyclones. On the contrary, the pressure trend in the centers of cyclones is negative, as is the trend in the duration of the impact of cyclones and anticyclones. It is shown that these trends underwent the most dramatic changes during 2012-2018, with a change of sign of the trend in pressure in the centers of anticyclones. Taking into consideration the close relationship between climatic characteristics and large-scale atmospheric circulation it can be suggested that the warming in Siberia before 2012 was due to a weakening of anticyclonic activity, and after 2012 it was due to an increase in cyclonic activity.

New results from studying the possible mechanisms of formation and degradation of the Chuya-Kurai ultra-high-pressure ice-dammed lake are presented. The conclusions are based on the analysis of the climatic hydrothermal regime which governs the development of the processes of self-freezing of the ice-dam and its subsequent degradation. According to updated data, at the maximum filling to the absolute level of 2133 m, the depth of the paleolake was 657 m, the volume of water was 753 km³, the water area was 3054 km², and the maximum hydrostatic pressure was 65 kg/cm² (6.37 MPa/cm²). The drainage of the lake basin was accompanied by the formation of 200 abrasive-accumulative terraces on the slopes of the basins in the height range of 1530-2133 m. A quantitative assessment of the formation time of one abrasive terrace in periglacial conditions is made as well as estimating the duration of the action of wind-wave processes for the development of abrasion: it did not exceed 90 days of a warm season. The water layers drained during the year through the thermal erosion channels of the ice dam were determined by the difference in the heights of the abrasive terraces. The duration of the existence of an ice-dammed lake has been clarified. The study used current quantitative data on measuring the average annual flow rate of the Chuya River at the nearest Chagan-Uzun hydrological post. Calculations have shown that the filling of the lake basin to the maximum volume of water of 753 km³ (taking into account the water accumulating in the ice dam, 68 km³ (total V = 821 km³)) was carried out for 5324 years. The duration of water discharge, determined by the number of abrasion terraces, was no more than 200 years. The frequency of retrogression of the lake level, equal to 20 years, has been revealed. Apparently, it was caused by climatic fluctuations: changes in cooling and warming.

Based on field expedition research and analysis of high-resolution polychronous satellite imagery data carried out in AlWaRes GIS environment, the latest data on the modern state of lake-glacial resources of Tsambagarav Ridge (Western Mongolia, Mongolian Altai), and their changes since the maximum of the Little Ice Age of the 17^th-19^th centuries were obtained. It was found that at the maximum transgressive stage of the Little Ice Age, with 3D topography of mountain-glacial basins taken into account, the glaciation of the ridge covered 99.1 km², and the total volume of glaciers reached 4.72 km³. The subsequent climate changes during the post-maximum phase of the Little Ice Age entailed a spatial transformation of the nival-glacial belt of the ridge, implying a progressive reduction in the size of the glaciation and the uplifting of its lower vertical limits. By August 2020, the total glaciation area of Tsambagarav Ridge decreased to 65.21 km² and ice reserves decreased to 2.98 km³. A statistical analysis of the mean annual air temperature of the northern regions of Western Mongolia over a half-century period showed a steady positive trend. A rise of annual air temperature was also accompanied by a decrease in temperature during the ablation period (June-August). In the modern deglaciation belt of the ridge, eight glacial lakes have appeared with a total water area of 0.34 km² and a water reserve of 1 260 000 t. Analysis of satellite imagery from 1966 to 2020 shows that most of them have formed in the last half a century and are confined to the pre-glacial margins of modern glaciers. Dependencies developed in the course of the study are used to calculate the indicators of intrastructural redistribution of water storage from glacial to limnic systems from the maximum of the Little Ice Age to 2020.

This paper presents the results of long-term expeditions which were aimed to study the occurrence of natural hybrids between Siberian stone pine (Pinus sibirica Du Tour) and Siberian dwarf pine (P. pumila (Pall.) Regel)). It was found that the ranges of these species are the most extensive among the five-needle pines, and they are located mainly in northern Asia. The eastern part of the Siberian stone pine range and the western part of the Siberian dwarf pine range overlap. Where both species grow together and the conditions for their cross-pollination are favorable, hybrids F1 are formed. It is shown that hybrids do not withstand competition with upright trees in phytocenoses typical for Siberian stone pine and are often damaged by snow piling. In phytocenoses typical for Siberian dwarf pine, hybrids show good growth, but are damaged due to frost weathering. It was found that the most favorable locations for hybrids are open sunlit areas where they form a balanced symmetrical crown and have abundant cone-bearing, but such locations are scarce. It is shown that the hybrid zone is characterized by mosaic structure, and in the northeastern and southwestern parts hybridization transforms into introgression. In the northeastern part of the hybrid zone, which coincides with the northeastern border of the Siberian stone pine range, hybridization has led to the replacement of Siberian stone pine by cryptic hybrids with the morphology of this species and mitochondrial DNA of Siberian dwarf pine, which are obviously more adapted to local conditions. In addition, it was found that hybrids growing in the south of Tomsk oblast are resistant to local climate and pests to the same extent as are parental species, and their unusual crown form, intermediate relative to the species, allows us to consider hybrids as an additional source of plant material for use in breeding work.

This article compares three methods of representing micro-charcoal analysis data for studying the thousand-year history of paleofires by using, as an example, microcharcoal data from the bottom sediments of Lake Uzunkol (Ulagan Plateau, Central Altai). The advantages of using the CC index of absolute concentration of microcharcoal per 1 cm³ (Charcoal Concentration) and the CI index for calculating the annual accumulation of microcharcoal per 1 cm² unit area (Charcoal Influx) in lake sediment samples in comparison with data on absolute counts of microcharcoal are proved. The results from applying the CC and CI indexes of microcharcoal to paleocharcoal data from bottom sediments of Lake Uzunkol, covering the time interval from the Late Glacial (17 000 cal. yr BP) till the present, are analyzed. The application of these indexes removes the artificial effect of the increased abundance of microcharcoal in the case of low pollen productivity of steppe landscapes. Results from studying paleomicrocharcoal in bottom sediments of Lake Uzunkol by using the three methods showed that natural fires in Central Altai were most intense in the Holocene during the transitional, unstable climatic period 9500-9000 cal. yr BP, when one type of landscape (steppe) was replaced by another type (forest). That is, forest-steppe landscapes were the most prone to natural fires in the past. By using the CI index, it was found that the development of ancient cultures in the Altai region was accompanied by a general increase in the concentration and accumulation of microcharcoal in lacustrine sediments, starting from 4500 cal. yr BP. A dramatic increase in the concentration and annual accumulation of microcharcoal occurred after 1700 cal. yr BP, which could be caused by an increase in population density in this region of Altai.

Methods for calculating vertical channel deformations based on hydrometric observations at the network of Roshydromet posts are considered. A method based on the relationship between water flow rates and levels is evaluated. It is concluded that the use of this method causes a number of serious difficulties and contradictions which do not allow its use in mass calculations. A method for assessing deformations based on using the lowest elevations of the channel is proposed. These marks are calculated from measurements of the channel simultaneously with the regular determination of water flow rates. The method was tested at 41 stations with a catchment area from 116 to 186 000 km² in the basins of the Angara, Upper Lena, Vitim, and Lake Baikal. The data were used for the entire observation period, with a duration of 35 to 80 years from 1943 to 2017. Vertical deformations are noted at all posts without exception. Their characteristic amplitude for the observation period is 50-150 cm. At one quarter of the posts, this value reaches 150-300 cm. The trend of deformations is multidirectional. In 41 and 39 % of cases, scouring and alluvium were observed, respectively. At the other posts, the trend is not pronounced. The calculations and the examples of their interpretation show the ability of the approach described to reveal various features of the process of vertical deformation of river beds. In particular, on its basis, it is concluded that there is a relationship between deformations and water flow rates when the same water flow rate on small rivers can produce tens of times more work of deformation of the channel bed than on large rivers.

This research has identified the landscapes in Chiapas State (Mexico) with the best natural conditions by using the theoretical-methodological principles of complex physical geography. To achieve this goal, the biodiversity was assessed by calculating the number of vascular plant species for each landscape unit and correlated with the results of previous research regarding landscape diversity and anthropization of vegetation cover. The results indicate that the highest levels of biodiversity correspond to the predominant and recurring landscapes. These geographical relationships indicate the influence of the geomorphological component on the distribution of biodiversity, which was quantitatively validated via two statistical correlations. It was found that the complexes of summits, hillslopes, and gullies in mountain landscapes of tectonic-karstic, tectonic-accumulative and tectonic-intrusive origin, in temperate, semi-warm humid to subhumid, warm humid, and warm subhumid climates, located in the physical-geographical regions of Lacandona Mountains, Southern Mountains of Chiapas, and Western Mountains of Chiapas, all have the most preserved physical-geographical landscapes. In recent years, however, geocomplexes have been impacted by society, which is particularly evident in the Northern Mountains of the Chiapas region. The results of this research are an important contribution to the land-use planning processes because they make it possible to objectively establish environmental policies in Chiapas. For instance, this research provides the geographic basis for modifying or promoting new natural protected areas.

A brief review of research and organizational and teaching activities of a famous geographer Yuri Petrovich Mikhailov, whose creative life activity is connected with the V.B. Sochava Institute of Geography, Siberian Branch, Russian Academy of Sciences (1961-2010). The fields of his scientific interests are considered: theory and methods of socio-economic geography, problems of nature management, peculiarities of the development of the domestic agrarian sector and rural areas, and integrated development of the taiga territories of Russia. A special place in Yu.P. Mikhailov’s scientific work is occupied by the issues related to the study, assessment and mapping of natural resources as well as geographical expert examination of major projects, the study of processes associated with the transformation of the habitat and the prediction of the consequences, and the protection and reproduction of the natural environment. It is explicitly pointed out that the wishers and message of Yu.P. Mikhailov’s scientific work to future generations of geographers imply their commitment to a system approach in geography. Presented is an extensive geography covered by the scientist’s research: Leningrad oblast, Crimea (subjects-polygons of his first field work) and, later, the territories of Siberia and the Far East. Qualitative and quantitative parameters of his publication activity and achievements in research and organizational activities are reflected. It is emphasized that the works of Yuri Petrovich Mikhaylov have an enduring theoretical and methodological, constructive and ideological significance.