Glacial Isostatic Adjustment Modulates Lateral Migration Rate and Morphology of the Red River (North Dakota, USA and Manitoba, Canada)

• Published in: Geophysical research letters 2023-08, Vol.50 (15), p.n/a
• Main Authors: Kodama, Samuel T., Pico, Tamara, Finnegan, Noah J., Lapôtre, Mathieu G. A., Willenbring, Jane K.
• Format: Article
• Language: English
• Subjects: Bends; Floodplains; glacial isostatic adjustment; Glaciation; Ice sheets; Meandering; Morphology; Red River; River banks; river dynamics on glacial timescales; River erosion; River meandering; River meanders; Riverbanks; Rivers; Sensitivity analysis; Shear stress; Slope; Slopes; Statistical analysis; Tributaries; U.S. midwest river geomorphology
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL103995

The lateral migration of a river meander is driven by erosion on the outer bank and deposition on the inner bank, both of which are affected by shear stress (and therefore channel slope) through complex morphodynamic feedbacks. To test the sensitivity of lateral migration to channel slope, we quantify slope change induced by glacial isostatic adjustment along the Red River (North Dakota, USA and Manitoba, Canada) and two of its tributaries over the past 8.5 ka. We demonstrate a statistically significant, positive relationship between normalized cutoff count, which we interpret as a proxy for channel lateral migration rate, and slope change. We interpret this relationship as the signature of slope change modulating the magnitude of shear stress on riverbanks, suggesting that slope changes that occur over thousands of years are recorded in river floodplain morphology. Plain Language Summary Rivers move through the landscape by eroding river bank material on their outer bank and depositing sediment on their inner bank, a process that forms meander bends. Understanding what factors drive river meandering is important for interpreting how rivers interact with landscapes. One factor that could impact river meandering is river slope. To understand the impact of slope on river meandering we quantify how slope has changed along the Red River (North Dakota, USA and Manitoba, Canada) over the past 8.5 Kyr. Over this time, vertical land movement substantially reduced the slope of the river, through the ongoing solid Earth response to the retreat of massive North American ice sheets in a process known as glacial isostatic adjustment (GIA). We find that change in slope, induced by GIA, positively correlates with river migration rate along the Red River, suggesting that slope plays an important role in determining the pace of river meandering. Key Points Glacial isostatic adjustment (GIA) is the primary control on slope change for the Red River (ND, USA and MB, Canada) since it began to flow 8.5 ka Slope change caused by GIA significantly correlates with river cutoff frequency, a proxy for lateral migration rate We infer that slope change modulates the magnitude of shear stress on the riverbank, driving changes in lateral migration rate