Episodic bedrock strath terrace formation due to meander migration and cutoff

Abstract

In order to explore mechanisms of bedrock terrace formation, we have developed a numerical model that couples vertical river incision and meandering. Model results illustrate that flights of unpaired strath terraces can form purely from the internal dynamics of bedrock river meandering in vertically incising channels. Specifically, knickpoints that propagate upstream following meander cutoffs enhance vertical incision, whereas channel lengthening and corresponding slope reduction during meander growth suppresses vertical incision. Analysis of topography from the Smith River, Oregon, USA, suggests terrace formation by this mechanism. Our results introduce an alternative mechanism to climatic or tectonic forcing, namely inherent instability triggered by meander growth and cutoff, that explains both oscillations in rates of vertical bedrock incision and the formation of longitudinally traceable, unpaired bedrock terraces. In addition, our results point to simple topographic criteria for identifying internally generated fluvial bedrock terraces.