Vol 54, No 2 (2023)

Until the end of the Late Pleistocene, the modern river valleys of most of Scandinavia remained buried under the cover of continental ice. The rivers of the region, including the Karelian ones, are distinguished by their geological youth, having formed as fluvial complexes only in the Holocene. The young age, combined with the strength of the crystalline rocks of the Baltic Shield, has affected the fact that the rivers here are characterized by the lack of development of the longitudinal profile. At the base of the thresholds, at which the flow acquires the character of rapid, the processes of formation of miniature scaffolds develop in places. A similar hydraulic situation developed at the front of the degrading glacier. The lower reaches of dams of hydraulic stations are also favorable for a powerful impact on the rock bed. Numerous traces of violent deep erosion, accompanied by the phenomena of indiscriminate erosion and hydrodynamic cavitation, can be found on the kilometer-long sections of the exposed rock bed of semi-mountain streams drained during hydraulic development.

A miniature scaffold developed by powerful natural and technogenically provoked floods in the lower part of the large rapid Matkozhnia on the Nizhny Vyg River, in the zone of the White Sea-Baltic Canal, is indicative. Almost the entire route of the canal, starting from Vygozero, is laid along the valley of the Lower Vyg. Only in some sections between the locks, the channel bed was dug away from the river. There, the old valley is preserved either almost dehydrated or with a small amount of water in the rock bed. The bedrock is exposed along the entire riverbed. Small boulders and pebbles of different sizes and grades of rolling can be found only in scattered pockets along the river channel. There numerous glass–like forms of microrelief – with a diameter and a depth of up to the first meters – “glasses” and “wells” are formed on Precambrian crystalline rocks. The contribution of evorsia to the denudation of crystalline slates in the bottom of the Vyga Valley on the rapid Matkozhnia is very significant, although the evorsion-cavitation effect itself is carried out rarely and for a limited time. Similar processes of natural origin operated before the creation of reservoirs on rapid-waterfall sites in the Vyga Valley and other large rivers of Karelia; they were caused by natural factors. Emergency descents of water through high spillway dams could increase the destructive effect of the stream on its root bed. So, in particular, the formation of evorsion microforms in the bed of the Lower Vyg at the rapid Matkozhnia is partially technogenically caused. Karelian cavitation-evorsion complexes of forms associated with hydrospheric catastrophes can be considered as miniature analogues of giant Late Pleistocene scablands of the northwestern USA.

The results of the morphodynamics analysis of denudation slopes and the coastal zone of Nagaev Bay, as well as estimated distances and rate of the eastern coastline retreat for the period from 1939 to 2016 are presented. The main methods of the work are morphographic and morphometric using aerial photographs of different years of flight, modern satellite images and snapshots. It is established that the morphostructure of the southern and northern shores of Nagaev Bay is determined by active faults striking in sub-latitudinal direction and framing the bay. The polygenetic mountain slopes adjacent to the coastline differ in length and angle of inclination. The slopes are covered with active kurums (stone runs) that slide towards the bay. In the lower part of the northern slope there is a zone of the Nagaevsky active fault, which causes a high dynamics of slope processes with a predominance of active kurums and landslides. The northern slope has been cut by a road built during the construction of the seaport and the Port Highway. As a result, widespread technogenically triggered landslides, rock falls and scree are often disrupting traffic on the highway. Thus, the territory of the commercial seaport and the Port Highway are at a risk of a sudden movement of large-volume of detrital material down the mountain slope. The eastern coastal zone is formed by a coastal ledge composed of unconsolidated deposits of the Nagaevskaya strata, an incomplete profile beach, and a littoral, the width of which reaches 200–250 m at low tide. The marine boundary of the zone runs at a distance of about 500 m from the coastal ledge. The eastern shore is actively moving towards the city of Magadan. During the period from 1939 to 2016, it shifted by 56 m with an average speed of 0.73 m/year. During the first stage (1939–1974), it advanced 29.0 m with an average speed of about 0.83 m/year. During the second stage (1974–2016), the coast moved for about 27.0 m with an average speed of 0.64 m/year. In recent years, large-scale work has been carried out on the eastern shore of Nagayev Bay in order to reinforce the shore and protect it from abrasion by erecting a breakwater wall. The engineering structure results in breaking of the established dynamic balance of coastal processes, which will eventually lead to the complete disappearance of the beach, and on the remaining unprotected sections of the coast – to increased abrasion and faster movement of the coastline towards the city.

The paleohydrological condition in the Rostov depression (Yaroslavl region) has been the subject of many years of discussions. The ideas about the Holocene fluctuations of the Lake Nero level differ among researchers. We have studied the structure of bottom sediments and bottom topography in the deepest northeastern part of the lake. A bathymetric survey was carried out. Drilling with the selection of undisturbed columns, GPR profiling, radiocarbon dating and a set of lithological analyzes were performed. Stratigraphic unconformities in the structure of bottom sediments indicate a drop in the lake level during the Lateglacial and the early Holocene. The level dropped to 87 m asl, which is 7 m lower than the current water level in the lake. The size of the lake at this stage was reduced several times. From 9 to 6.5 ka BP a transgressive stage was established: the average level of the lake could have risen to 91–94 m asl, which is close to its modern level. From 6.5 to 2.4 ka BP a decrease in the level by 1–3 m below the current one is revealed, followed by a gradual increase in the level. The current level was reached 300–500 years ago. The main factor in the fluctuations in the level of Lake Nero in the Holocene is the change in the height of the runoff threshold, caused by the transformation of the Ustye, Veksa, and Kotorosl river sistems. This transformation was associated both with regional changes in fluvial activity and with the processes of self-development of river channels.

The article presents the results of the first comprehensive study of the structure and morphology of the glacial relief of the Gorodok Upland in the north-eastern Belarus. New data were obtained using lithological-stratigraphic, petrographic and morphometric methods. It has been established that the formation of the upland is predetermined by the uplift in the top of the Upper Devonian rocks. This uplift of the pre-Quaternary surface is overbuilt by Middle Pleistocene glacial deposits with glacial tectonics and erratic masses. The presence of an uplift led to the formation of the upland in the ice divide zone between the Chud and Ladoga Ice Streams during the last glaciation. As a result, during the maximum advance of the last ice sheet, a moraine plateau with kames began to form in the center of the upland. During the Lepel Stage (18–20 cal. ka BP, Edrovo in Russia, Gruda in Lithuania, and Poznan in Poland) the ice lobes of the Chud and Ladoga Ice Streams moved from the periphery to the moraine plateau. In total, there were six distinct oscillations of the glacial edge. As a result, chains of hummocky and ridge end-moraine landforms were formed. Later, during the Braslav Stage (16–18 cal. ka BP, Vepsa in Russia, Baltija in Lithuania and Pomeranian in Poland), hummocky end-moraine landforms were formed on the north-western and north-eastern slopes of the upland. At the same time, large runoff troughs crossing the upland from the north to the south were formed as a result of ice melting. The results of the study are important for the rational conduct of geological surveys and prospecting for mineral building materials within the ice-divide zones of the last glaciation.

Based on the interpretation of satellite images and field observations, three moraines of different ages and morphology were identified in the valley of Ev’vayam River. The oldest, poorly preserved and significantly eroded moraines are located in the lower reaches of the Ev’vayam River near the Bering Sea coast. A well expressed in relief complex of younger moraines consisting of three better-preserved moraine ridges (45, 62–72 and 87–95 m a. s. l.) with thin soil cover is distinguished in the middle reaches of Ev’vayam River. The youngest moraines are found in the upper reaches of the Ev’vayam River Valley at elevations of 240–320 m a. s. l., where they form longitudinal ridges, or “tongues”. Based on the preservation degree, morphology and size of the investigated glacial complex, and published data on adjacent areas, the glaciation of the territory had a mountain-valley character. The glacier apparently reached its maximum size at the beginning of the Late Pleistocene, when it moved beyond the valley of the Ev’vayam River to the coast. The moraines in the central part of the valley and in its upper reaches were formed by much smaller glaciers during the end of Late Pleistocene. The recharge area of glaciers during this period was limited to a series of glacial cirques and kars in the central part of Pylgynskiy Range. Currently, small glaciers are present in cirques at elevations from 410 m to 720 m a. s. l., and continue to form modern moraines.