INTEGRATING NEWLY AVAILABLE LIDAR-DERIVED IMAGERY DURING COMPLETION OF A GEOLOGICAL MAPPING PROJECT, ONEIDA COUNTY, WISCONSIN

A study of the Quaternary geology of Oneida County in north-central Wisconsin, including the preparation of a 1:100,000 geologic map, is nearing completion. The study of this densely forested area was conducted using standard field techniques including the interpretation of available aerial photography with results plotted on 1:24,000 U.S. Geological Survey topographic quadrangles. A LiDAR-derived 5-foot resolution countywide digital elevation model (DEM) was constructed from data that became available from USGS as the mapping of the last four of more than 20 quadrangles was underway. The high resolution DEM and resultant hillshade image provided an opportunity to refine our understanding of the geologic history, landscape evolution, and geologic mapping of the entire county.

The hillshade image revealed to us previously unrecognized landforms and their distribution, and this in turn influenced our interpretations of the geologic history of the area. New interpretations included the recognition of previously unseen deposits of ice-walled rivers, deltas, lake basins, shore-ice-collapse trenches, and channels that defined a complex system of rivers and lakes that were the drainage system in the late glacial, largely ice-cored landscape. We were also able to refine the mapping of drumlins, both those at the surface and those draped by meltwater-stream sediment, many of which were small and masked by tree cover. Many previously unrecognized ice-walled-lake plains were also identifiable on the imagery but not on aerial photography or topographic maps. Studying the imagery led to few changes of the contacts defining the extent of genetic material units on the geologic map that were delineated prior to acquisition of the DEM.

LiDAR-derived DEMs are publically available for only one third of Wisconsin counties. Our understanding of the geologic history of previously mapped areas will be refined as more LiDAR-derived DEMs become available. For example, LiDAR-derived DEMs and hillshade images for previously mapped areas to the north and south of Oneida County allowed the reevaluation and refinement of many aspects of the regional geology including the distribution of landforms marking ice-margin positions during deglaciation, late-glacial drainage systems, and the sequence of landscape stabilization.