EVIDENCE, UNCERTAINTY, AND IMPLICATIONS OF RHEOLOGICAL CONTROLS ON SURFACE PROCESSES

The rheological properties of the lithosphere are increasingly recognized as having a quantifiable influence on the rates and patterns of surface processes. Strain localization, controlled by the mechanical response to local tectonic and topographic stress fields, manifests as planar fault damage zones that impose predictable displacement, strength, and grain size distribution patterns across the Earth’s surface. Evidence for this dependency exists in 1) the strong directional dependence shared between structural features and drainage network patterns, 2) consistent experimental results suggesting an inverse proportionality between rock plastic strength and erosion rate, and 3) the inverse proportionality between grain size and channel carrying capacity. However, there is still significant uncertainty in how the mechanical properties scale to erosional processes. We test the sensitivity between rock mechanics and erosion by incorporating two mechanical properties of rock, plastic strength and fracture density, in a landscape evolution model. Three plausible scaling rules are used to frame the uncertainty in linking strength to erodibility, and we assume power-law fracture density/ grain size distributions that scale with strength. Based on sensitivity analysis, naturally occurring rock strength values can exert significant controls on the rates and patterns of landscape development and adjustment when using a conservative scaling rule. Drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion and transport of fault gouge. The resulting topography retains information about the rheology and mechanical properties of the underlying lithosphere through their distinct controls on relief, directional dependence, and erosion rates.