The Niger River is one of the largest rivers in Subequatorial Africa. River channel classification developed by Lomonosov Moscow State University was applied to define variations in Niger River channel. The main channel type along the River Niger is braided, conjugated, with complex of terraces. The new groups of types of river channel have been identified that were not previously identified in the Subarctic, Moderat, Subtropical zones of Eurasia. The inclusion of “African” species in this classification is explained by the large differences in rainfall between the wet and dry seasons in the Subequatorial zone. New morphological varieties are terrace braided reaches and barrage braided channel reaches, meandering floodplain lake-channel systems and floodplain lake-channel disconnected systems.

This article presents the model of scale-level organization of subrelief (“relief” of underground cavities) based on its genesis. There are 2 morphodynamic levels of subrelief evolution: underground morpholithogenesis (underground cavity formation) and imposed morpholithogenesis (formation of secondary landforms without significant changes of underground cavities). Morpholithogenesis is a process of synchronous formation of sediments and landforms or forms of subrelief. Further classification of suggests two hierarchical levels based on genesis and scale of landform formation. Scales are used according to the size of formed subrelief. These hierarchical levels of morpholithogenesis represent the balance of cavity genesis and her internal dynamic. Stages of W. Davis’s geographic cycles have been chosen as relative time units. Youthful stage corresponds to initial formation and active expansion of the underground cavity. The imposed subrelief actively evolve (for example stalactites and stalagmites in karst caves) in the cavity during mature stage. Then the cavity is being destroyed inside and eventually collapses at the old stage. This concept links the evolution of underground (sometimes semi-underground) cavities with “classical” surficial relief into a natural or natural-technogenic system and should be used as basic method to study subrelief.

A huge number of different anthropogenic (man-made) landforms have been created in the valleys and riverbeds, which have transformed their appearance and the nature of erosion-accumulative processes. Major landforms that have a long-term impact on the landscapes of river valleys include large dams, regional multikilometer dikes and main canals. Large forms disturb the longitudinal and transverse connectivity of the river system. This intervention in the relief of river valleys completely transforms it, as well as the direction of the geomorphological processes. There are also smaller-scale landforms that belong to the river relief and play an important role in the river morphology and dynamics due to their wide distribution and indirect consequences they exert. This category of anthropogenic forms covers a wide range of engineering structures and activities that, being exposed to the action of a water flow and interacting with it, develop and transform according to the laws of nature, they can be called natural-anthropogenic forms.

A comparative analysis of lake area distributions for lacustrine thermokarst plains and thermokarst plains with fluvial erosion has been performed using he mathematical morphology of landscapes and remote sensing. We applied mathematical models of landscape patterns for lacustrine thermokarst plains and thermokarst plains with fluvial erosion under the “synchronous start” of the thermokarst conditions. Twenty-two key sites were included in the empirical testing. The empirical testing involves 22 key sites. These sites have different geomorphological environments within the areas of either continuous and discontinuous permafrost or sporadic permafrost. We have theoretically revealed and validated it empirically that in different natural environments, the lake area distribution within lacustrine thermokarst plains generally corresponds to the lognormal distribution while the gamma-distribution is almost absent. On the contrary, the model shows that lake area distribution within thermokarst plains with fluvial erosion generally corresponds to both the lognormal and gamma-distributions. This result does not exclude different scenarios of lake area distribution patterns for the plains with fluvial erosion under an asynchronous start of the thermokarst. The empirical testing proves the validity of the mathematical models of that the morphological patterns for the lacustrine thermokarst plains and thermokarst plains with fluvial erosion under the synchronous start of thermokarst processes. Therefore, different techniques should be used for the quantitative assessment of the impact probability of the thermokarst processes on engineering structures for the lacustrine thermokarst plains and thermokarst plains with fluvial erosion. The mathematical model used in this study proved to be a good instrument for such assessment.

Three belts of ice-marginal deposits have been determined in the south-west part of the Kola Peninsula. They correspond to three phases of the Scandinavian Ice Sheet retreat in the Late Pleistocene. Clast fabric analysis and lithological investigation of the glacial deposits and morphometrical analysis of the glacial relief allowed to determine glaciodislocations of squamous-thrust and folded type in the ice-marginal complexes. Arrangement regularities of ice-marginal deposits in the region were defined using morphometrical study of present relief. The squamous-thrust glaciodislocations were found in structure of the first and second belts of the ice-marginal deposits. They correspond to single large ridges or massifs of parallel ridges. Particular fragments represented by low ridges with glaciofolds at their cores formed from loose sediments from the base of the ice-sheet. The third belt of ice-marginal deposits consists of folded marginal tills and rarely squamous tills interbedding with fluvioglacial deposits. In present relief this belt is represented by ridge-hummocky and hummocky forms and its characteristic feature is deltaic fluvioglacial deposits on the distal end of eskers. Analysis of clast fabric and glaciodislocation structures identified that during the formation of the first and second ridge belts glacier had been moving mainly east along the White Sea Basin. At the time of formation of the third belt active glacier had been advancing south and south-eastwards. Each phase of glacier retreat was accompanied by short-term oscillatory dislocations. In the White Sea Basin and on the moraine plain glacier degradation was fast and had areal character. Frontal type of deglaciation existed on the convergence areas of the ice-marginal complexes. The new data on structure of the glacial deposits, for the first time executed study of structure and clast fabric analysis of glaciodislocations, and morphometrical characteristic of relief allowed to reconstruct dynamic of the last glacier cover on one of the key areas of the Kola region.

The results of studies of relationship between populated areas infrastructure (rural and urban) and erosional relief, gully erosion and channel processes are generalized. The formation of infrastructure and living conditions of the population depend on the degree of territory dissection by ravine-gully and river network, location of settlements on river banks – from small to the largest. Most of the settlements are confined to rivers and large gullies with a permanent watercourse, because these landforms supply water, ideal for industry development, energy production and transportation. At the same time, gully erosion and channel migration create certain risks for disfunction or destruction of operating facilities. With the growth of settlements and development of their technical and economic potential, the impact on certain elements and on the entire erosional relief is expanding, and the protection from hazardous gully erosion and channel processes is necessary. At different stages of their existence, settlements may completely depend on the relief, adjust to or transform erosion and channel processes, neutralizing their negative impact on human activities. Sustainable development of settlements depends on adequate choice of the territory, rational use of the erosional relief features, and accounting for probability of changes in the course of channels and gully formation. The study present the assessment and general classification of relationship of urban and rural settlements infrastructure (from small rural to the largest cities) with erosional relief, gully erosion and channel processes. Cities and rural settlements, subordinated to or suppressing erosional relief, rivers and channel processes are distinguished. The larger the city, the more complex these relationships are. Within the large city, different areas may refer to different types of interaction.

Organic matter content was analyzed in 10 sediment cores retrieved from different parts of Lake Ladoga using the loss on ignition (LOI). The thickness of retrieved sediments varies from 0.7 to 1.7 m. The lower part of the sediment sequences was formed in the Late Pleistocene – Early Holocene, or during the Holocene climatic optimum. Up to five periods of organic sedimentation were recognized in all studied cores. Two periods of higher organic content were distinguished corresponding to the Mid Holocene and the recent 1500 years, respectively. The first maximum in the Mid Holocene ends with a sharp decrease in the content of organic matter; a decrease in organic matter occurred before the beginning of the second maximum. All recognized periods are believed to primarily result from changing productivity of the Lake Ladoga ecosystem, which relates in turn to climatic changes during the Holocene. Among regional-scale paleogeographic events (transgressive and regressive stages of the Baltic paleobasins, Ladoga transgression) only the Baltic Ice Lake stage and its regression can be clearly recognized in changing organic sedimentation. Lake-level changes resulted from the Early Holocene Ancylus transgression and the Mid Holocene Ladoga level rise are less visible in the organic matter content. Similar trends in organic concentrations can be identified in all studied sediment sequences even though some of them are incomplete. Since the changes in organic matter content are often not expressed in lithology, this approach can be applied for correlation of the sediment sequences from different parts of the lake.

The bottom of the trough of Zhom-Bolok River along the entire length (about 70 km) was covered by flow of basaltic lavas about 13 ka BP. At present, extensive debris cones formed by river’s tributaries that mainly composed of debris flows material are developed on top of the lava flow. Eighty cones with a total volume of 210 million m³ were recorded in the valley; the largest of them are located in the middle and lower reaches of the river, where they occupy from 15 to 25% of valley’s bottom surface area. During the last 13 ka the average denudation rate in the catchment areas of the Zhom-Bolok River’ tributaries, draining Kropotkin Ridge, was 0.024 mm per year. Obviously, this rate is only the average minimum, because in some cases, the cones of larger streams are partially washed away by the river. Soil development and forest coverage on the debris cones at present indicate that at present the debris flow activity is low. According to research data in the adjacent territory, the peak of debris flow formation activity occurred at the beginning of the Holocene. Along with the effusion of lavas, the removal of significant volumes of loose material by tributaries influenced the morphology and development of the Zhom-Bolok river valley. In the post-eruptive period, the runoff initially went through lava tubes. It is partially preserved to this day. Cones development caused the filling of lava cavities with loose material, preventing the intralava drain, and promoted the formation of lakes at the bottom of the valley and the displacement of the river channel. The total incision of the river into the lava flow during the post-eruptive stage reached 6–7 m. During floods, an erosive floodplain is actively formed in the valley, including due to erosion of the distal parts of the cones. The results of petrographic and mineralogical analyzes of the Zhom-Bolok river channel alluvium suggest that currently it is mostly dominated by material carried by tributaries with the content of basalt fragments not exceeding 10%.

Olympus Mons (basement dimension – 550 × 600 km, absolute height – 21.1 km, relative elevation – 21.9 km, volume – 2.4 × 10⁹ km³) is the largest volcanic edifice on Mars as well as on Earth. Comparative analysis, aimed to find the regular combinations between volcanic and glacial forms at Olympus Mons revealed their similarity to terrestrial volcanic landform, tuya. This, probably, testifies to their similar origin. Olympus Scarp, 3–6 km in height, bounding Olympus Mons, suggests that, during the formation of Olympus Mons vast glaciers existed beyond the polar regions. The distribution of extensive glacial moraines allowed to estimate the area of glaciation to be equal to 1.5–2 × 10⁶ km², as well as ice sheet thickness of 3–6 km, comparable to the recent height of Olympus Scarp. Several moraine lobes point to multiple phases of glaciations. The directions of the lobe propagation record the asymmetry in glaciers distribution. Edge of the glacier was located 700–750 km away from the crater in the South-western, Western, North-western, Northern, and North-eastern section of the volcano, and 500–600 km away elsewhere. Some of the glacial and fluvioglacial deposits disperse to the maximum extent of 1100 km, probably by giant mud flows, similar to terrestrial Jökulhlaup in Iceland ice-covered volcanoes. Such floods form when the heated during the eruption water melts the ice wall around the erupting vent and outbursts from the volcanic edifice.

Year 2020 is the 100^th anniversary of the birth of O.K. Leontiev, the Russian scientists, geographer, one of the founders of coastal geomorphology, marine geomorphology, and physical geography of the World oceans. Leontiev was the founder of the University School of Marine Geomorphology. He was the first to develope training courses in marine geology for oceanology students, geomorphology of coasts and ocean floor for students – geomorphologists, physical geography of the ocean for physical geography students. The Caspian Sea with variety of tectonic conditions and a changing sea-level regime was chosen by him and his colleagues as a natural laboratory. In addition, he carried out expeditionary studies along the coast of many seas and during long ocean voyages. This paper gives an overview of the main scientific achievements of Professor O.K. Leontiev.

Georgy Vysotsky, outstanding Russian geographer, is remembered by his valuable contributions in the development of physical geography, soil science, geobotany, forestry, forest restoration, hydrology, climatology, hydrogeology and zoology of Russia. G.N. Vysotsky’s scientific views was influenced by Vasily Dokuchaev, a giant figure of Russian geography, who’s main principle was to study nature as a single and undivided whole looking at it through the eyes of geographer. Vysotsky was a talented scientist and a no less talented practical worker who taught how nature could be changed to fully fit the interests of man. However, his contribution to geomorphology have not been fully studied and summarized yet. This article fills the gap: it contains and analyzes his original cartographic geomorphological materials: a map of the river basins of the European part of Russia, detailed orographic map of the Ergeni, a map of precipitation, winds and air humidity in July; a summary map of resultant winds of Ukraine; a map of combination of the soil and relief plans of the Sarepta district, a map of dry steppes of European Russia as well as the geobotanical profile across the eastern slope of the Ergeni. Georgy Vysotsky created a series of new scientific terms that are widely used today: illuviy (illuvium), mikrorelief (microrelief), plakor (flat interfluve), impulverizatsia (saltation), psevdofibry (dense horizons), desuktsia (desuction), permatsidnye pochvy (percolative regime of soils), digressia (pasture digression), demutatsia (pasture restoration), areny (arenas), ekotop (ecotope), etc.