RIVER CHANNEL PATTERNS IN MOUNTAINOUS COUNTRIES AND BEDROCK LITHOLOGY

Abstract

A river channel in mountainous countries is controlled by two main factors: 1) tectonic activity of the terrain; 2) lithology of bedrock defining its characteristics of weathering; by latter criterion the majority of rocks has been divided into two main types: break-stone and block ones. Easily erodible rubbly bedrock supplies rivers with affluence of fragments having the same sizes as bedload sediment. That is why incision gives way to lateral erosion at relatively high valley gradients, and a river, being locally overloaded with sediment, acquires the braided pattern. In bedrock of the blocky type, the supply of bedload sediment is scanty; progress of erosion cycle is slow; as a result valleys with low gradients and meandering channels are worked out. The data on the distribution of river channel types in the eastern Russia confirm the concept discussed.