Dynamic Equilibrium Between an Active Uplift and the Sevier River, Utah

Abstract

In a zone of active tectonic uplift, one expects a river to change morphology simply because valley slope deforms. But by cutting through a transverse uplift, the Sevier River in southern Utah also adapts to the tectonics by eroding and depositing. These localized changes of transport are caused by varying channel geometry, pattern, sedimentology, and slope. In the uplift, the river is narrow, efficiently shaped, coarser‐grained, and expends a greater proportion of energy on bed particles. It deposits sediments downstream in exaggerated meandering reaches with wider, less efficient channels. Localized erosion and deposition create a dynamic equilibrium with the structural growth, but this equilibrium includes nonlinear responses like knickpoints and depositional lobes. In response to the required erosion and deposition, the river so dramatically alters channel grain size and channel geometry that the increase of sinuosity expected in the tectonically steepened valley does not occur.