Sediment cover modulates landscape erosion patterns and channel
steepness in layered rocks: Insights from the SPACE Model
Abstract
Erosional perturbations from changes in climate or tectonics are
recorded in the profiles of bedrock rivers, but these signals can be
challenging to unravel in settings with non-uniform lithology. In
horizontally layered rocks, the surface lithology at a given location
varies through time as different layers of rock are exposed. Recent
modeling studies have used the Stream Power Model (SPM) to highlight
complex variations in erosion rates that arise in bedrock rivers
incising through layered rocks. However, these studies do not capture
the effects of coarse sediment load on channel evolution. We use the
“Stream Power with Alluvium Conservation and Entrainment” (SPACE)
model to explore how sediment cover influences landscape evolution and
modulates the topographic expression of erodibility contrasts in
horizontally layered rocks. We simulate river evolution through
alternating layers of hard and soft rock over million-year timescales,
with a constant uplift rate of 1 mm/year. Compared to the SPM, model
runs with sediment cover have systematically higher channel steepness
values in soft rock layers and lower channel steepness values in hard
rock layers. As sediment cover effects increase, the contrast in
steepness between the two rock types decreases. Effective bedrock
erodibilities back-calculated assuming the SPM are strongly influenced
by sediment cover. We also find that sediment cover can significantly
increase total relief and timescales of adjustment towards
landscape-averaged steady-state topography and erosion rates.