PATTERNS OF STEEPNESS IN WALLOWA RIVERS

When rocks are uplifted to form mountains, one of the processes that alter the shape of the mountains is the incision of rivers. The tectonic uplift in an area will alter the river profiles. Depending on the type of uplift there could be knickpoints, the rivers could alter to an unusual shape, or the there could be a small lake formed at the location of faulting. Patterns of river morphology can provide insight into the patter, style, and timing of tectonic uplift.

We analyzed river profiles from 25 drainage basins in the Wallowa of northeast Oregon to explore the patterns of uplift in this mountain range. The first step in collecting data was to calculate flow accumulation and delineate drainage basins using ArcGIS. The data was then brought into MATLAB to extract the river profiles within the drainage basins. Patterns in channel steepness (local channel slope normalized for contributing drainage area) are then plotted across the Wallowa. One problem with this is that the rock lithology may not be uniform across the landscape; the rivers may thus be steeper or shallower for a given erosion rate and drainage area depending on the substrate composition. To account for this, we compare maps of channel steepness with a geologic map to distinguish between tectonic and lithologic knickpoints. The resulting patterns of inferred tectonic knickpoints are compared to different models of the tectonic evolution of the Wallowa region.