Feedbacks between Knickpoint and Divide Migration as Reflected in Paired Reverse and Truncated Channels

Drainage reorganization is a primary pathway for landscape adjustment to varying tectonic and climatic constraints. Reorganization occurs via processes of drainage divide migration that are typically driven by differential erosion rate caused by differences in slope across the divide. Whereas such differences in slope are often attributed to upstream knickpoint migration in response to changes in base level, the interactions between knickpoint and divide migration remains largely unexplored. Such interactions are expected because the drainage divide location determines the drainage area and discharge that drains across the knickpoint, and thus the rate of knickpoint retreat. The knickpoint lip, on the other hand, sets the local base level for channel and hillslope processes next to the divide and thus can influence the rate of divide migration. To explore this potential feedback in a well constrained setting, we focus on drainage reversal toward cliffs, where drainage divide migration along pre-exiting paleo-valleys causes a 180 degrees change in the flow direction, so a knick-point is formed where the reversed channel flows down the cliff. We analyzed reversed channels along cliffs in Appalachia, Brazil, West Africa, and the Middle East and quantified patterns of divide migration over long and short time scales using chi and slope imbalance across the divide, respectively, and also modeled simple end members of this process. Our preliminary findings suggest that the short and long term trends of divide migration are generally consistent, and that differences in chi and slope imbalance between reversed channels likely reflect different magnitudes and/or temporal stages in the feedback between the divide and knickpoint migration.