Bulletin of the RAS. Geography

The results of long-term geological and geomorphological field work on the Kuril Islands (Kunashir, Iturup, and Paramushir islands) and Kamchatka Peninsula have shown significant activity of denudation processes in thermal fields and surrounding areas, among which landslides and erosion are the most common. The laboratory studies indicate that gas-hydrothermal alteration of rocks in geothermal regions results in a significant change in their composition, weakening and decrease in strength. These factors contribute to the gravitational displacement in slopes, often with blocking of river valleys. Slope displacement and failure is additionally activated by the thermal water discharges and soils heating. Geothermal areas often have numerous traces of debris flows, often non-seasonal. The activation of linear erosion on exposed slopes can result in the formation of baldlands areas. Watercourses draining thermal fields can carry away significant amounts of suspended and dissolved material. It leads to an increase in denudation rates and the formation of erosion-denu-dation funnels and denudation basins in areas of hydrothermal explosions. It also causes an abnormal expansion of watercourse valleys within thermal fields compared to background areas. Our observations allow us to draw conclusions about surface deformation in geothermal fields, which is caused by the natural migration of thermal fluids and the exploitation of thermal deposits. Obviously, there is need to continue research of the geothermal areas at the Kuril-Kamchatka region using a wide range of geological, geomorphological and cartographic methods, including the innovative technologies such as radar interferometry.

A quantitative assessment of soil erosion factors and intensity was carried out for the Asian Russia over the 2015–2021 period, with a spatial resolution of 100 meters. The results were subsequently generalized to small river basins. Rainfall erosion was evaluated using the USLE/RUSLE model. Melt runoff was assessed using the methodology of the Soil Erosion and Fluvial Processes Research Laboratory at Moscow State University. New approaches to estimating the erosion factor were implemented for the first time in this macroregion: the erosive potential of rainfall (R-factor) and the vegetation cover factor (C-factor). The R-factor was estimated based on developed statistical models utilizing intra-day precipitation data collected by Roshydromet meteorological stations, as well as spatial covariates derived from remote sensing data. The C-factor was calculated monthly using multi-temporal remote sensing data providing information on land cover types, vegetation density, spectral vegetation indices, and phenological metrics (products from CGLSLC, Fcover, MOD13Q1, MYD13Q1, and VNP22Q2). This is the first time that a modern estimate of the snowmelt erosion factor—the maximum (pre-spring) water reserves in snow—has been obtained in this macroregion. This assessment used the CGLS SWE satellite product, which is derived from remote sensing data. The annual soil erosion intensity across the entire macroregion averaged 3.1 t per ha per year, with a median of 0.045 t per ha per year. On the limited arable lands within the region, erosion rates averaged 1.8 t per ha per year, with a median of 0.54 t per ha per year.

The purpose of the work is the origin of the ridges of the Tobol-Ishim interfluve, linearly elongated, subparallel landforms, oriented from northeast to southwest, formed on different elements of the ancient relief. This topical issue has been the subject of discussion in the fields of geomorphology and paleogeography for many years. In order to achieve this, it was necessary to reconstruct the conditions of formation and age of the ridge deposits using field and analytical methods (granulometry, morphoscopy, specific magnetic susceptibility and cryogenic contrast coefficient). The ridges are everywhere composed of yellowish-brown, low-sorted fine sand with a large proportion of clayey and silt components. This indicates their accumulation in uniform aeolian conditions. This is confirmed by the results of morphoscopy of quartz grains (the proportion of particles with traces of aeolian action ranges from 68-72 to 100%), enveloping parallel layering, constant values of specific magnetic susceptibility according to the profiles of ridge sections, the same orientation of ridges, the rare occurrence of paleontological remains, and blowing basins. The ratio of blowing basins with the crests and hills located to the east of them reflects the predominance of westerly winds during their formation. The upper part of the ridge sections is a facies difference of cover loess-like sediments, with a sharp lower boundary overlying the underlying sediments of different origin and age. The ridge strata differ from inter- and extra-ridge sediments due to the different dynamics of sedimentogenesis and hypergenesis. In the upper parts of the ridge sections, the effect of cryogenesis on sediments is especially noticeable. The proportion of quartz grains with traces of cryogenic impact ranges from 36-68 to 64 - 96%. During the formation of ridges, the climate changed from moderately humid to cold arid. Low cryogenic contrast coefficient values are indicators of seasonal permafrost and positive average annual soil temperatures. Single high cryogenic contrast coefficient values are witnesses of continuous permafrost, low soil temperature, the existence of landscapes of cold semi-deserts and deserts. By the method of optical-stimulated luminescence from ridge sediments, dates in the chronointerval from ~34 to ~26 hours. years ago were obtained.

The Rostov Lowland features numerous ancient paleochannels that are clearly visible on satellite images and are located outside the meandering belts of the main rivers. Notably, three generations of paleochannels larger than the current river meander are associated with the Usty–Kotorosl river system. The reasons for their increased size, their isolation from the modern river network, and the presence of multiple generations remain unclear. Resolving these questions could shed light on the historical development of the lowland during the Late Pleistocene and Holocene, including establishing connections between paleochannels and nearby lake Nero. This study examines the morphometric parameters of these paleochannels, comparing them with modern river meanders. It analyzes longitudinal profiles along the channels and floodplains of both ancient and modern rivers, offering hypotheses about past configurations of the river network and factors driving its reorganization. The findings indicate that most paleochannels are approximately two or three times as large as their modern counterparts–distinguishing them from other large paleochannels within the Volga River basin. A new review of remote sensing data enabled a comprehensive tracing of a paleochannel through which the Usty River once flowed into Lake Nero's basin. Small meander cirques within this paleochannel have parameters similar to those of current river meander. The increase in the catchment area of Lake Nero led to the formation of large paleochannels by the Vyoksa River. The small size of modern meander in the upper reaches of the Kotorosl River has previously led to misinterpretations regarding paleochannel sizes. The characteristics of longitudinal profiles along the Usty–Kotorosl river system suggest that change of the Kotorosl River's valley occurred relatively recently, transitioning from its ancient to modern river valley.