Basin Properties and Postglacial Erosion Rates of Minor Moraines in Iowa

Two minor moraine basins in Story County, Iowa, were examined to determine the extent and effect of postglacial erosion on the present landscape and stratigraphy. Minor moraines are subtle repeating ridge and valley landforms with relief of approximately 2 m. The stratigraphy was examined in this study using grid and transect borings. A mantle of locally derived postglacial sediment blanketed the Late Wisconsinan till in both basins. In places, a strata of coarse diamicton separated the till and sediment. The postglacial sediment was identified primarily on particle size distribution and bulk density. After determining the extent and thickness of sediment in each basin, the sediment volume and mass were calculated. Previously, the Late Wisconsinan till in central Iowa was dated as being deposited 14 000 RCYBP (radio carbon years before present). This age was used to calculate a gross annual rate of postglacial erosion. The basin with modern relief of 2.7 m had a 0.9 Mg ha −1 yr −1 erosion rate and the basin with modern relief of 1 m had a 0.7 Mg ha −1 yr −1 erosion rate.