Bedrock valley morphology and tributary basin organization records signatures of lithology and transience across the Upper Mississippi River Valley
Abstract
Bedrock river valley morphology (e.g. relative valley width and valley relief) records the relative influence of lateral erosion and vertical incision. These relative rates of vertical and lateral incision can be influenced by local lithology, uplift, climate and glacial history, and sediment supply. Previous studies have demonstrated that bedrock valley aspect ratio, Wv*, at a cross-section can be a reliable metric to characterize these effects. The Upper Mississippi River Valley (UMRV) presents a case study that encompasses a wide range of valley forms, from narrow bedrock gorges to widely beveled floodplains. These variations in bedrock valley aspect ratio are likely due to a combination of spatially variable glacial history, lithology, and drainage reorganization. These factors may also influence the development of first order tributary basins to local baselevel change and differential channel incision. This research aims to discern the relative contributions of lithology, downstream changes in drainage area, history of reorganization, and variability in glacial isostatic adjustment on bedrock valley and tributary basin morphology across the UMRV. To explore downstream variability in bedrock valley aspect ratio, we extract valley width, and valley relief from digital elevation models at 100m intervals from Minneapolis to Thebes Gap (n= 13020). We find considerable variability in bedrock valley aspect ratio, with wv* ranging from <25 to >300. Valley aspect ratio adjusts in response to lithologic transitions or drainage reorganizations. Perhaps most notably, we observed a local 200% increase in wv at the Mississippi-Missouri Confluence due to the combined effects of the added catchment area and the transition to more erodible shale bedrock. Additionally, we extract tributary basin area, steepness, and Hack's Law exponents for all first-order tributary basins draining to the floodplain. We observe spatial variation in basin area and slope across the UMRV. Spatial patterns in valley aspect ratio and first-order tributary basins may serve as reliable recorders of geologic, climatic, and tectonic history in large river basins where aggradation occludes the extraction of bedrock long profiles. We suggest that these metrics may offer a more +integrated look at transient adjustment in large river systems.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMEP35D1363D