A NEW LOOK AT THE IOWAN EROSION SURFACE AS A MEGAFLOOD LANDSCAPE

The Iowan Surface landform region is an area of low relief, covered in a mantle of loamy sediments above a distinctive coarse-grained sand or gravel base. Early workers described water-laid sediments, but later interpretations have called upon glacial processes, periglacial processes, or soil formation to explain this enigmatic landscape.

The geomorphic features of the Iowan Surface, including extensive boulder trains, areas of exposed bedrock, deeply incised bedrock gorges, amphitheater-headed canyons, streamlined paha hills, and the distribution of loess, resemble similar features found in the Channeled Scablands of western Washington and other landscapes now recognized as having been shaped by megafloods. The proximity of Glacial Lake Agassiz, the location of its southern outlet, and the alignment of Glacial River Warren and the modern Minnesota River with the dominant northwest-southeast fabric of the modern drainage network of the Iowan Surface suggest a possible source of floodwaters. The Big Stone moraine and other glacial deposits, and exposed and eroded bedrock in southern Minnesota, may have been the source of sandy sediments and giant erratic boulders of the Iowan Surface region.