Dynamic bedrock channel width during knickpoint retreat enhances undercutting of coupled hillslopes

Mountain landscapes respond to transient tectonic and climate forcing through a bottom-up response of enhanced bedrock river incision that undermines adjoining hillslopes, thus propagating the signal from valley bottom ridges. As result, understanding mechanisms set pace pattern is critical first step for predicting wider landscape evolution. Typically, focus has been on impact channel bed lowering by upstream migration knickpoints angle, length relief with limited attention role dynamic width. Here, we present suite physical model experiments show direct knickpoint retreat reach-scale width, across range flow discharges (8.3 50 cm3 s?1) two sediment (0 0.00666 g cm?3). During retreat, width narrows as little 10% equilibrium while shear stress >100% higher immediately compared conditions. We only fraction narrowing can be explained existing hydraulic theory. Following passage knickpoint, returns lateral erosion widening. For tested height, demonstrate adjustment process more significant hillslope stability than elevation change, highlighting importance considering both vertical in evolution models. It therefore important understand key processes drive knickpoints, localized geometry ongoing implications hillslopes supply network export onto neighbouring depositional plains.