UNDERSTANDING THE TIMING AND GEOMORPHOLOGICAL CONTROLS ON HOLOCENE UPSTREAM AVULSIONS AND SUBSEQUENT CHANNEL BELT DEVELOPMENT: LOWER MISSISSIPPI RIVER, USA

Deciphering the controls and necessary geomorphological conditions needed to initiate channel avulsions and subsequent channel belt development on single-thread alluvial bed rivers is presently an important topic of discussion amongst geomorphologists and engineers. River avulsion is the single most important process controlling the distribution of sediment and water across depositional basins, and governs the location of the depositional center of sediment mass within a basin through time. Presently, researchers are very interested in understanding the intricacies of river avulsion in order to (a) determine where to build sediment outlet channels along coastal plains in order to combat coastal land loss, and (b) gain insight into the large scale alluvial architecture of basin fills in order to optimize natural resource recovery. Recently collected Optically Stimulated Luminescence Dates (OSL) from the St. Francis and Yazoo Basins within the lower Mississippi alluvial valley (LMV) coupled with preliminary numerical modeling efforts have uncovered both the timing and spatial distribution of upstream Holocene river avulsions along the lower Mississippi River, USA (LMR). The results of both OSL dating and theoretical numerical models suggest that the important factors determining both the timing and spatial distribution of Holocene LMR avulsions is dictated by (i) base-level rise after the Last Glacial Maximum (LGM) between ca. 10.0 to 4.0 ka, (ii) the spatial allotment of Pleistocene sand bodies within the LMV, and (iii) floodplain morphology and longitudinal changes in width controlled by local bedrock outcroppings within the LMV.