FACTORS INFLUENCING MORPHOLOGICAL CHANGES IN AN ALLUVIAL REACH OF THE MISSOURI RIVER VALLEY DURING THE LATE HOLOCENE:IMPLICATIONS FOR RIVER SENSITIVITY TO CLIMATE CHANGE

Detailed mapping of the Missouri River Alluvial Valley using allostratigraphic techniques reveal four contrasting meander morphologies over an alluvial reach spanning the Miami Station, Malta Bend, Carrollton East, Carrollton West, Grand Pass, and Waverly quadrangles in Missouri. Distinctions between the meander morphologies are based on differences in their channel width, channel depth, meander wavelength, meander radius, and bar grain size. All morphologies occurred since 2500 b.p., and reflect changes in river pattern with time caused by natural factors. Factors potentially influencing morphologies are: 1) discharge variations from the catchment; 2) local tectonic controls on valley gradient; 3) composition of sediments delivered from the catchment; and 4) bank vegetation as a control on the bank stability. The extent of these effects argues against local tectonic control. The remaining three are dictated by climate, and suggestive of high sensitivity of the river to short-term late Holocene climatic change in the continental interior. These changes are on the scale of late Holocene temperature excursions affiliated with the little Ice Age and Medieval Warm and could be driven by such events. Likewise, these could record effects of late Holocene “megadroughts.” High sensitively of the river to climate change could have strong influence on ongoing efforts to plan reclamation of the river to accommodate needs of both commerce and habitat because 1) current river morphology cannot be considered stable over very long time spans, and 2) foundational substrate materials for habitat are non-uniform in the valley.