26 Karst Hydrogeologic Systems of the Central United States and Northern Mexico

Monday, 12 April 2010
1:30 PM - 5:15 PM
Short Creek 2

THE USE OF HISTORIC AERIAL PHOTOGRAPHY TO IDENTIFY PALIMPSEST KARST TERRANE IN ILLINOIS' SINKHOLE PLAIN

Paper number: 26-4
Program: Theme Sessions
Time: 2:10 PM – 2:25 PM

Authors

Abstract

Karst features such as cover-collapse sinkholes in areas dominated by row-crop agriculture in southwestern Illinois’ sinkhole plain can become totally obscured over time. It is clear that land use practices in this region have changed the physical landscape, specifically where cover-collapse sinkholes have been plowed over and/or filled in so many times that they are no longer visible. As a result, the surface terrain can take on a palimpsest karst appearance; that is, the sinkholes can become quite difficult to identify or can be all but completely obscured. Such is the case in Illinois’ sinkhole plain.

In the course of characterizing the karst features of the sinkhole plain in southwestern Illinois, we observed palimpsest karst terrane. In order to thoroughly map the karst terrane, we used historical aerial photography. We found that 1940 vintage aerial photography (taken during a very dry period) was particularly useful when compared to more recent 2005 aerial photography. A comparison of the 1940 photography with 2005 photography revealed that at least 10% of the sinkholes were no longer visible on the 2005 photographs, and were not present on USGS 7.5 minute quadrangle maps. The dryness of the land shown in the 1940 photographs highlights the sinkholes so that they appear as white rings concentrically surrounding a dark center. The light-colored rim areas consist of dry soil, whereas the darker, deeper centers of the sinkholes are wetter. After decades of using modern, large-scale farming equipment and the widespread adoption of conservation tillage methods beginning in the 1980s, many clearly defined sinkholes visible on 1940 aerial photographs are indistinguishable on 2005 aerial photographs. Conversely, early, leaf-off acquisition photography of wooded areas in the 2005 photography reveal abundant sinkholes that are not visible in the leaf-on 1940 photography because they are masked by the tree canopies

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