NEW ESTIMATES OF THE AREAL EXTENT OF PLEISTOCENE LAKE TIGHT BASED ON GIS MAPPING AND ANALYSIS

Proglacial Lake Tight was first mapped in detail by Wolfe (1942). Based on several lines of evidence, Wolfe mapped the extent of Lake Tight at the 900-foot elevation contour, which was derived from 50 USGS topographic maps. The areal extent of Lake Tight founded on Wolfe’s reconstruction is estimated to have covered 7,000 square miles (Hansen, 1995). Today, we have technological mapping advantages Wolfe did not, including Geographic Information System (GIS) technologies and Global Positioning Systems. In this study, topographic contours obtained from raster elevation datasets available from the USGS National Elevation Dataset (NED) database were utilized to reconstruct proglacial Lake Tight in a GIS. ArcGIS was used to convert the NED datasets into discrete contour elevation feature classes. Using a number of GIS geoprocessing utilities, the 275-meter contours (902 feet) were processed to create one seamless feature class. In addition, the contours were spatially correlated with Ohio Department of Natural Resources’ glacial, geologic, and topographic GIS datasets to delineate the boundaries for the Lake Tight map. Based on the GIS reconstruction, a revised estimate for the extent of Lake Tight was calculated, suggesting the lake was approximately 40% greater in size than previously estimated. The advantages of integrating the Lake Tight map within a GIS provide for a wide range of geological and geomorphological spatial queries, performance of exacting calculations, development of 3D models, and output of data in a variety of digital and hardcopy formats. The GIS model of Lake Tight has broad implications for further studies, as some of the map elements have been spatially queried to corroborate significant geologic landforms believed to have been formed during the development of Lake Tight (see Bailey, Bishop, and Shoemaker, this conference).