Semester of Graduation
Master of Science (MS)
Geology and Geophysics
It has long been recognized that bedrock streams gradually adjust their slopes towards topographic steady state, an equilibrium state between rock uplift rate and erosion rate. Tectonic geomorphology studies often analyze stream profiles for clues of this adjustment, which can initiate from changes in tectonic and climatic forcings. The stream power incision model, the most widely utilized framework with which to interpret bedrock stream profiles, predicts that streams perturbed from topographic steady state by changes in bedrock erodibility or uplift rate adjust their slopes to return to topographic steady state through upstream propagating waves of incision, or knickpoints. Under the assumptions of uniform bedrock erodibility and topographic steady state prior to a change in boundary conditions, these knickpoints are predicted to propagate upstream at uniform vertical velocities and celerities set by the stream’s erodibility and contributing drainage area. Using a commonly employed 1-D model, this study tests the validity of steady state assumptions of knickpoint behavior when stream profiles are influenced by non-vertical contacts. Deviations in the behavior of knickpoints from steady state assumptions are found to increase as a function of the contact’s along-stream celerity and change in erodibility. This results from non-vertical contacts acting as non-stable base levels that alter the uplift rates to which upstream reaches adjust. While this study evaluates highly simplified model scenarios to assess knickpoint elevation, celerity, and prominence as a function of contact dip, change in erodibility, change in uplift rate, and stratigraphy, it demonstrates that steady state assumptions of the stream power incision model break down upstream of non-vertical contacts separating reaches with contrasting rock erodibility.
Wolpert, Joshua A., "Response of Transient Base Level Signals to Erodibility Contrasts in Bedrock Streams" (2020). LSU Master's Theses. 5183.