Slope Break and Avulsion Locations Scale Consistently in Global Deltas

Understanding how deltas respond to changing sea level is crucial as deltas provide important ecosystems, are inhabited by ∼500 million people, and are nexuses of food, energy and economic activity. The response of delta distributary channels to sea‐level rise depends on the geomorphic controls on delta morphology and their scaling relationships. Our data from 105 deltas globally show strong scaling between the upstream distances to slope breaks and to avulsion nodes, and confirm the previously known scaling between backwater and avulsion lengths. The break in slope is proposed to be the principal control on delta development, along with other proposed secondary controls. We identify and discuss the implications of this slope break‐avulsion length scaling, leading to a conceptual model of delta morphology and sedimentology. This model suggests how deltas may respond to future sea level rise and guides interpretation of deltaic deposits in the rock record. Plain Language Summary River deltas across the globe are being affected by sea‐level rise. How deltas respond to this rise is thought to be related to a region (known as the backwater zone) where the river flow velocity starts to decrease due to river slope reducing as the flow approaches the sea. The location of this zone has been shown to scale with the location of abrupt shifts (known as avulsions) in the position of delta channels. However, we do not have a complete understanding of why and where these shifts occur. By analyzing 105 river deltas globally, we found that the strongest scaling relationship is between the distances from the shoreline of avulsion and of a change in slope. Due to this strong scaling relationship, we propose that river deltas may respond to sea‐level rise differently depending on their shape and gradient, and the location of the slope change on the delta itself. Key Points Morphometric boundaries investigated in 105 modern deltas globally Slope break and avulsion lengths show the strongest scaling relationship, more significant than previous scaling relationships Processes contributing to this slope break‐avulsion length scaling relationship are proposed along with conceptual model of the implications