DEVELOPMENT OF THE MINIATURE ANALOGUE OF THE SCABLANDS OF THE WEST USA IN THE LOWER POOL OF ONE OF THE KARELIAN HYDROELECTRIC POWER STATIONS¹

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.