Erosion dynamics in carbonate bedrock channels inhibit weathering processes

Abstract

The interplay of rock weathering and erosion processes controls the erodibility of bedrock. Existing models of these processes in bedrock river channels have been developed using observations largely from silicate lithologies, neglecting the effects of the dissolution of soluble carbonate minerals. Here, we present a study of rock erodibility in two limestone bedrock channels in the North Pennines, UK. Patterns in rock erodibility were assessed using Schmidt hammer surveys conducted in 12 cross-sections and were analysed alongside calculations of bedrock inundation interval, observations of sediment transport from bedload impact plates and long-term estimates of limestone dissolution rates from environmental data. Results show that erosion via dissolution can result in similar patterns of rock erodibility observed in silicate channels where erosion outpaces weathering. Bedrock inundation interval is a key control on bedrock erodibility, although to a lesser degree than channels in silicate lithologies. Where the channel margin is not regularly inundated by flow, weathering processes which weaken the rock are still present but may be locally offset by dissolution driven by soil seepage of low pH runoff which erodes weathered material. Furthermore, we do not always observe the expected impacts of weathering and erosion on channel geometry, with channel geometry seemingly more sensitive to the availability of abrasive tools (sediment supply). Long-term estimates of abrasion and dissolution rate are broadly equivalent at our study site further demonstrating the effectiveness of dissolution at eroding carbonate lithologies, although further work is needed to isolate feedback between these two variables. Future studies of bedrock incision processes in carbonate landscapes should re-evaluate how mechanical erosion and dissolution are represented, and how sensitive the balance of these processes is to potential changes in inundation frequency and climate.