IOWA'S MEGAFLOOD? A CIRCUMSTANTIAL CASE FOR FORMATION OF THE IOWAN SURFACE LANDFORM REGION

The Iowan Surface landform region is an area of low relief covered with a mantle of loamy sediments above a distinctive coarse-grained sandy or gravelly base. The origin of the Iowan Surface has long been considered enigmatic, although many alternative mechanisms have been proposed for its formation. Examination of geomorphic features, including distribution of erratic boulders, distribution of areas of exposed bedrock, distribution and thickness of loess, streamlined paha hills and associated sediments reveals similarities to the Channeled Scablands and other areas that are now recognized as having been shaped by megafloods since LGM. The proximity, size and volume of Lake Agassiz, the location of its southern outlet, and the alignment of the Minnesota River valley with the dominant northwest-southeast fabric of the Iowan Surface drainage network suggest a possible source of floodwaters and sediments.