GIS-based Reconstruction of the Zion Beach-ridge Plain, Illinois, based on Historical Maps, Aerial Photographs, and a LiDAR-derived DEM

Abstract:

The Zion Beach Ridge Plain (ZBRP) is located along the open, wave-dominated southwestern Lake Michigan coast. The gradual migration of post-glacial lake-margin deposits has produced dozens of ridges, whose orientations and depositional architectures have yet to be fully understood. Ongoing work is aimed at studying how late Holocene climates and lake hydrology have influenced ridge development. In contrast to embayed strandplains of the Great Lakes region, the ZBRP is more exposed to high-energy wave/current conditions, offering potentially unique insights into process-landform dynamics.

GIS-based mapping was employed to compartmentalize and reconstruct the architecture of the ZBRP. Aerial photographs, which provide locations of former shoreline positions and capture vegetation patterns, chronicle landform development since the 1930s. NOAA-derived nautical charts and USGS topographic maps extend this record to the 1860s. A high-resolution LiDAR-derived DEM was used to create a detailed lineament map of the strand, by which morphometrics were extracted from the former for analysis.

A total of 41 distinct beach ridges have been mapped across the ZBRP. Preliminary results show that the southern, actively growing part of the system is compartmentalized into morphologically-distinct sets: 1) S-trending and shore-parallel ridges (the youngest); 2) SW-trending and shore-oblique ridges; and 3) Topographically subdued ridges furthest from shore (the oldest). Shore-proximal ridges are bracketed by known shoreline positions while C-14 ages of sampled swale deposits offer constraints on older parts of the ~3kyr-old strand. A near-complete geomorphic history of ~1.5 kyrs should exist here, assuming a constant rate of growth (based on post-1860 data).

Continued refinement of an absolute ridge chronology is needed to evaluate the potential for beach-ridge metrics (e.g., height) to serve as hydrographic and paleoclimatic proxies at the ZBRP. Tree heights, canopy characteristics, trunk diameters, and dendrochronological data may offer additional insights into the timing of ridge development beyond constraints of historical information. This would allow ridge patterns to be evaluated in context of regional climate records using absolute ages as temporal benchmarks.