OUTCROP MAPPING IN ARGYLE LAKE STATE PARK USING LIDAR SLOPE MAPPING

In glaciated terrain, like that found over much of Illinois, finding rock outcrop for study is incredibly difficult. However, being able to locate such outcrops not only facilitates study of the geological history of the area, but also can help provide local areas for use in geological education (the primary driver of this project). The irregular surface of the bedrock essentially represents the land surface at one time with new land surface draped over the top. The geomorphology of the surface can provide some clues as to where outcrops lie; hillsides supported by rock tend to maintain steeper slopes with the underlying rock to support them. Thus, we propose that by examining the slope in an area known to have bedrock close to the land surface, we should be able to predict outcrop locations based on the distribution of slope.

A slope surface was created from the LiDAR Digital Elevation Model (DEM) for Argyle Lake State Park (McDonough County, Illinois). We then mapped the distributions of slope and field tested the map to see at what values of slope outcrop tended to occur. We found that slopes of 60° or higher tended to be very good predictors of the location of outcrop (or strata immediately below the surface). This method, when applied to areas relatively undisturbed by humans, may provide an effective way to generate a preliminary outcrop map and help identify sites for further geological study.