Effects of erosional resistance on bedrock channel occurrence and morphology: Examination of the Seo River catchment in South Korea

Abstract

In tectonically stable regions, bedrock channels develop along deep and narrow valleys that are usually associated with resistant lithology, which enables the transport capacity of these channels to exceed the upstream sediment supply. However, bedrock channels are not restricted to the reaches with a high transport capacity. They are often located in reaches with a lower transport capacity in wide valleys underlain by erodible bedrock. Even though bedrock channels are distributed over a wide range of lithologies, the effects of erosional resistance on the transport capacity required for bedrock channel formation have not been fully clarified. We investigated the bedrock channels in the Seo River catchment in South Korea to determine the relationship between erosional resistance and the occurrence and morphology of bedrock channels. We found that more than half of the bedrock channel segments were in resistant regions. However, a considerable portion also occurred in erodible regions. Most of the bedrock channels in the resistant regions were steep and narrow, generating a higher unit stream power. Therefore, these channels had long stretches of exposed bedrock with actively eroded features such as well-abraded surfaces. In the erodible regions, most of the bedrock channels were wide and gentle, leading to a lower unit stream power. Thus, the exposed bedrock surface was poorly polished, and the channel morphology preserved more of the underlying bedrock's joint or bedding structures. These results suggest that erosional resistance affects the occurrence of bedrock channels by adjusting the threshold stream power required for bedrock incision. Moreover, lithology strongly regulates the bedrock channel morphology in erodible regions.