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Iowan erosion surface
The Iowan Erosion Surface (IES) is a geographic region located mostly in northeastern Iowa while extending into southeastern Minnesota. The IES is a former enigmatic curiosity because its topographic relief and other elements about it seemed to fit the criteria used for the identification of glacial, fluvial and eolian landforms. The entire region is covered and built out of very thick pre-Illinoian till which is a very old till with an age of 790,000 years and older. A thin blanket of loess covers the till in places. The relief of the IES is a widespread, vast plain dotted in many areas with streamlined, elliptical hills called paha while the orientation of the whole region and its relief is NW-SE (northwest to southeast).
==Hypotheses==
Early thinking at one time designated this region as the "Iowan Drift" while its landforms were believed to be glacially-formed in nature. Later-thinking somewhat improved on this past hypothesis about the paleo-processes responsible for the origin of formation but was divided into two schools of thought: running-water erosion 〔Ruhe et al., 1968〕 and combinatorial slopewash and eolian (deflation) erosion.〔Prior, 1991〕 Current thinking now places the IES within the concept of Pleistocene wind-deposition of snow and subsequent snowmelt erosion.〔Iannicelli, 2010〕 These processes are encompassed within the periglacial realm of the Pleistocene because of the proximal positioning of the ancient continental ice sheet that laid nearby to the region of the IES which was just outside of the adjacent Driftless Area region.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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