Landscape Evidence of Fault Zone Architecture in the Southern Sierra Nevada

Abstract:

In equilibrium, Earth’s landscape reflects a balance between rock uplift and erosion. This balance causes geomorphic landforms, such as hillslopes, watersheds, and stream channels, to maintain steady-state geometries that reflect the rate of rock uplift, the erodibility of the underlying bedrock, climate, and the surface processes that formed them. Departure from equilibrium, due to changes in these boundary conditions, causes the landscape to adjust until a new steady-state geometry is established. Geomorphic features can therefore be used as indicators of tectonic activity in areas where the underlying geology, climate, and dominant surface processes can reasonably be assumed to be uniform. In this study, Revs-Up participants utilized ArcGIS^® and Matlab^® software to characterize key geomorphic features in the southern Sierra Nevada Mountains of eastern California. Watershed boundaries and river longitudinal profiles were extracted from USGS 10m digital elevation models and used to plot watershed slope vs. area relationships. These plots were then used to determine profile concavity and channel steepness index values for watersheds along the southern Sierra Nevada Frontal Fault Zone (SNFFZ). Initial results show a northward increase in the complexity of river longitudinal profiles as well as a northward increase in channel steepness indices. Normalized channel steepness index values are highest within watersheds located along a prominent left step in the Sierra Nevada rangefront. Combined with field data and low-temperature thermochronometry, these results may help to constrain spatial variations in rock uplift associated with the long-term evolution of the southern SNFFZ.