Vol 55, No 1 (2024)

Comparison of the longitudinal profile of a number of lowland rivers in Russia, revealed their deformation due to a half-century of sediment flux and channel morphology adjustment. This problem remains relevant both in theoretical and practical aspects, especially for rivers where long-term mining of sediments from the stream beds extends from kilometers to tens of kilometers. The removal of a large amount of alluvial material from the sediments transport and changes of the riverbed morphometric characteristics triggered the process of leveling the sediment transport capacity along the river by the scour and resulted in a lowering of the bottom and water surface. The intensity of the incision reached 3–8 centimeters, and its progradation along the river 400–700 meters per year. Retrogressive erosion is pronounced, while progressive one is less pronounced, because partially replaced by mechanical removal of alluvial material. Over the past decades the shape of the longitudinal profiles changed from convex or straight to concave with no signs of recovery, despite the mining has been quite moderate for last 30 years or completed on the explored rivers.

The results of a study of channel displacement for 2000–2022 in 55 key areas located on rivers of different orders, draining across different landscapes of Udmurtia, are presented. The erosion rates were determined using benchmarks and tacheometric survey. To analyze the obtained results, the rivers were divided into 4 groups based on their order magnitude (according to the method of A. Scheidegger). Maximum erosion rate (up to 15 m/year) is typical for rivers of an order higher than 14, 6–8 m/year for medium rivers with an order of 9–14, 5.5 m/year for small rivers with an order of 6–9, and up to 4.2 m/year for very small rivers (of order 6 or less) under natural conditions and up to 8.1 m/year with man-made intervention. The mean annual and maximum amount of erosion were calculated for each reference areas for the period of observation. Correlation analysis showed a high significant relationship between the erosion rate and river order and, accordingly, the average annual and maximum discharges. The connection between the values of erosion and the annual amount of precipitation was found only for 3 small rivers within the Kilmez River basin. Trend analysis of erosion over a 23-year time interval was performed for the selected groups of rivers.

Improvement in quality of digital elevation models and satellite images of the Earth’s surface led to a tendency to interpret them without sufficient confirmation by geological research methods. At the same time, the geological data is critical for the interpretation of genesis of accumulative glacial landforms and regional landscape reconstruction during the last glaciation. The article provides a classification and geologic structure of the glacial relief of one of the key areas in the Kola region. New data were obtained using morphometric analysis of relief, geological, structural analysis of glacial landforms, petrographic analysis of coarse glacial deposits, and the study of lake sediments. Two bands of glacial accumulative relief were identified in the study area.

The first band forms a parallel ridge relief on the southern slope of the Lovozero Tundra. It represents the formations of a lateral moraine formed at the edge of a glacier moving from the west to the east along the slope. Also a hummocky-ridge relief along the slopes of the Lovozero, Panskie, and Fedorova Tundras that consist of terminal moraines is included in this band. The moraines are composed of dislocated limno- and fluvioglacial deposits, dump and ablative moraines.

The second band is formed by three subparallel chains of ridge-hummocky relief. They include folded and imbricated-thrust glaciotectonically deformed deposits. Fluvioglacial deposits are developed on the distal slope of the outer chain.

Both bands of glacial relief are associated with formation of marginal landforms during two stages of glacial retreats. Analysis of deglaciation models of the last ice sheet in the Kola and adjacent regions and data on the position of known marginal glacial formations made it possible to compare the stages with the final episodes of the Luga (Karelian) and Neva (Syamozero) Stages. The information obtained reveals more details about the stages of development of the last ice sheet and the deglaciation pattern of the Kola region in the Late Glacial.

The Late- and post-glacial history of the development of the White Sea coastal zone in the area of the Varzuga River mouth is considered as a result of the interaction of endogenous and exogenous factors of coastal morpholithogenesis. Based on geomorphological investigations, study of Holocene deposits by lithostratigraphic, diatom and radiocarbon analyses, as well as collection and analysis of published data, new results on the area’s relief development for ~13 cal ka BP have been obtained. The features of the regional hierarchical morphostructure and local post-glacial tectonics of the territory — the spatial relationships of blocks and the speed of vertical movements – were determined. The superimposed linear Nizhnevarzugskaya depression, which determined the configuration of the Varzuga River estuary in the late and postglacial time, was identified for the first time. The influence of the spatial ratio of blocks and differentiated postglacial uplift on the coastal morpholithogenesis was established. The course of changes in the relative sea level (RSL), development conditions and morphodynamics of the open coast and the estuary of the Varzuga River were reconstructed and new data on the rhythms of coastal morpholithogenesis processes (coastal, estuarine, and aeolian) obtained. Three stages of the coastal zone development were identified, corresponding to regional rhythms of changes in the relative sea level and climate: (I) Late Glacial transgression and Early Holocene regression (~12–9.8 cal ka BP), (II) Middle Holocene Tapes transgression (7.8–4.9 cal ka BP), (III) Late Holocene regression (after 4.9 cal ka BP). The upper marine boundary of the Late Glacial transgression is traced at the elevation of ~54–55 m a. s. l. to the west of the Nizhnevaruzgskaya depression, — ~39–40 m a. s. l. to the east of it, and — 22–25 m a. s. l. in the depression. The shores of lower morphostructural blocks were probably blocked by dead ice up until ~10.2–9.8 cal ka BP. During the Tapes transgression, the RSL reached a maximum (~7.8–7.6 cal ka BP; ~20 m a. s. l.), and by 4.9 cal ka BP fall to ~15 m a. s. l. The prevailing directions of sediment fluxes, winds and wave approach became similar to those of today. However, the main source of the coastal zone sedimentary supply was the erosion of glaciofluvial sediments and the input of sands from the seabed. In the interval of ~4.9–1.7 cal ka BP, the RSL decreased to ~5 m a. s. l. The sediment runoff of the Varzuga River became the main source of feeding the coastal zone.

The chronology of the Mikulino Interglacial and its individual phases have been the subject of discussion. The goal of this study was to evaluate the time limits of the main stages of the Mikulino Interglacial on the Russian Plain according to ^²³⁰Th/U dating and paleobotanical studies of lake and peat sediments from the known sections located within the Tver region on the Bolshaya Dubenka River, Malaya Kosha River, Granichnaya River, and Sizhina River (“Kileshino-2” section). An improved geochronological approach has been applied to identify layers suitable for the ^²³⁰Th/U isochronous approximation. In combination with pollen and carpological studies of the deposits, this made it possible to date units corresponding to relatively narrow time intervals in the development of plant formations at different stages of the Last Interglacial. New paleobotanical studies of buried lake and peat sediments from the sections located on the Bolshaya Dubenka River, Malaya Kosha River, and Granichnaya River allowed us to restore the vegetation development during the Mikulino Interglacial in the interval of pollen zones M1–M7, i.e., more pollen zones have been analyzed and in greater detail than in 1960–1970. A chronological scheme of the main stages of vegetation development in the Mikulino Interglacial is proposed based on the results of ^²³⁰Th/U dating and paleobotanical studies of organic-rich deposits from the Tver region sections in combination with previously published data obtained for the “Nizhnyaya Boyarshchina” section from the Smolensk region. The Mikulino Interglacial had begun about 130–126 kyr ago. Its first phase, corresponding to the M2 zone, ended ca. 118 kyr ago. The pre-optimal stages of vegetation development (M3 and M4 zones) fit into the time range of ca. 118–112 kyr ago. The climatic optimum of the interglacial (M5 and M6 zones) began ca. 112 kyr ago and ended ca. 100 kyr ago. The duration of the Mikulino Interglacial was probably at least 25 thousand years.