VISUALIZATION AND ANALYSIS OF GLACIAL RETREAT IN NEW YORK USING ArcGIS APPLICATIONS

The great ice sheet covering northern North America began a rapid retreat near the end of the Pleistocene Epoch. The retreat history of the eastern Mohawk Valley and the central Hudson Valley, New York, is well documented in an illustrated NYSGA field guide article by Robert G. LaFleur in 1979. A series of hand-drawn figures shows the sequence of ice retreat, and associated glacio-fluvial and glacial lake deposits for the last several thousand years of the Wisconsin Stage. In an effort to visualize the retreat sequence in digital form, a series of digital maps were created using ArcGIS desktop applications, which can be directly compared to the hand-drawn maps of LaFleur.

Digital Elevation models (obtained from the USGS seamless data warehouse) were used to create the desired features in each of the six images in the sequence. The DEM was reclassified into specific features based on elevation classes, including ice limits, water ways and lakes. This was done by creating a new raster based on a polygon element using the Extract by Mask tool located in the special analyst tool box. After the desired raster images were created, depositional features such as deltas and lake sediments were added as polygons to each image.

When one compares each digital image with its corresponding hand-drawn image, remarkable similarity and accuracy of feature boundaries and positions is clearly evident. Very minor differences were noted in small tributary waterway positions in the final images, which could be attributed to differences in modern DEM data versus older topographic data.