Iowan erosion surface
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The Iowan Erosion Surface (I.E.S.) is a geographic region located mostly in northeastern Iowa while extending into southeastern Minnesota. The IES is a former enigmatic curiosity because its 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).
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  and combinatorial slopewash and eolian (deflation) erosion. Current thinking now places the IES within the concept of Pleistocene wind-deposition of snow and subsequent snowmelt erosion. 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.
Action of wind
An anticyclonic wind system hovered over the continental ice sheet that blew snow-bearing winds from out of the northeast towards the southwest. The winds shaped the snow into transverse NW-SE trending snow dunes. These in turn, carved out NW-SE linear to curvi-linear snow dune meltwater valleys/depressions and its complementary NW-SE snow dune meltwater interfluves.
Blankets of snow
The plain of the IES are actually pediments  which are now perceived as originating from the more familiar blankets of snow which caused sheetwash erosion over the (paleo)permafrost resulting in Pleistocene cryopedimentation (and cryoplanation). This flattened out the lowlands while leaving behind remnant snow dune meltwater interfluves (hills) which would be the paha.
Although inselbergs are commonly perceived within an arid to semi-arid "hard-rock geology" environment, they can also be perceived within the paleopermafrost environment because the Pleistocene till was hardened into rock-like masses. Likewise, the "classical" inselbergs of arid to semi-arid pediments can be equated to the unlithified, paleopermafrost paha of the cryopediments belonging to the IES.
- Ruhe et al., 1968
- Prior, 1991
- Iannicelli, 2010
- Iannicelli, 2000; 2003; 2010
- Hallberg et al. 1978
- Iannicelli, 2010
- Hallberg, G., Fenton, T.E., Miller, G.A., Luteneggar, A.J. (1978), The Iowan Erosion Surface, an important lesson and some new wrinkles. In, "Geology of East-Central Iowa", R.R. Anderson (ed.), Iowa Geological Survey,42nd Annual Tri-State Geological Field Conference, Guidebook, pp. 2.2 - 2.94.
- Iannicelli, M.(2000), Snow dune erosion and landforms. Northeastern Geology and Environmental Sciences, vol. 22, no. 4, pp. 324 – 335.
- Iannicelli, M. (2003), Devon Island's oriented landforms as an analog to Illinois-type paha. Polar Geography, v. 27, no. 4, pp. 339 – 350.
- Iannicelli, M. (2010), Evolution of the Driftless Area and contiguous regions of midwestern USA through Pleistocene periglacial processes. The Open Geology Journal, v. 4, pp. 35 – 54.
- Prior, J.C. (1991), Landforms of Iowa. University of Iowa Press, Iowa City, 153 pp.
- Ruhe, R.V., Dietz, W.P., Fenton, T.E., Hall, G.F. (1968), Iowan Drift problem, northeastern Iowa. Iowa Geological Survey, Report of Investigations, v. 7, 40 pp.