Development of the upper reaches of erosion systems in the Russian plain in the area of the moscow glaciation

The headwaters of the river systems on the East European Plain between the boundaries of the Late Valdai (Marine Isotope Stage 2 – MIS 2) and the Moscow (MIS 6) glaciations developed during the last 150,000 years. During this time, there were at least three climatic episodes characterised by very high relative to modern surface runoff causing intense deep and backward erosion: at the end of MIS 6, in the second half of MIS 2 and in the middle Holocene. Watersheds cut by erosion systems have a mosaic geological structure, from hard-erodible glacial tills (moraines) to low-resistance sandy deposits. In moraines, the main deepening of erosional forms occurred in pre-Holocene time. Even relatively large forms such as balkas (dry valleys) have not yet reached concave longitudinal profiles. The general trend of their development was deepening. Short episodes of incision, occurring during climatic intervals with increased water flow, alternated with long periods of stabilisation. In the Holocene, the largest erosion events associated with episodes of anomalous intensity of atmospheric precipitation (probably heavy rainfall) are dated to the time interval from 6 to 3 thousand years ago. In different parts of this interval, single gullies appeared in areas with sufficiently high gradients and sandy substrates. These gullies quickly reached their ultimate size and now have graded concave longitudinal profiles. All other gullies cutting through moraines and bedrock were formed in pre-Holocene time, but are still far from being graded and have convex, convex-concave and stepped longitudinal profiles. The diversity of catchment areas, initial slope gradients, and properties of the geological substrate that determine its resistance to erosion has led to great differences in the evolution of the upper reaches of river systems within the Moscow glaciation area compared to the more homogeneous landscape conditions of the extra-glacial areas of the Russia Plain.