Morphological Interpretations of Glacial Forms by Spatial Analysis in the Area Surrounding Lake Simcoe, Ontario

Abstract

Drumlins are sedimentary geological features that indicate the final direction of glacier movement; as a result, they are of great interest in understanding past glacial events. In southern Ontario alone, thousands of drumlins have been mapped and interpreted remotely through the use of aerial imagery or topographic maps. These are often paired with digital elevation models (DEMs) and/or contour maps offering detailed information about the area of study. This paper presents the results of a change-detection study that used maps of different vintages of the drumlin-rich area around Lake Simcoe in southern Ontario. Two topographic maps and two DEMs, each with contours at 25-ft (7.6-m) and 10-m intervals, were compared in three regions: (A) the urban region in the city of Orillia, overlying sand plains; (B) the area east of Orillia, on top of clay plains; and (C) the region south-east of Lake Simcoe, overlying till plains. The 7.6-m contour topographic maps and DEMs display comparable levels of detail; however, over time the drumlins appear to erode, likely a product of the underlying sediment in combination with urbanization. The 10-m contour topographic maps display less detail than DEMs of the same resolution, suggesting that the popular topographic maps are not the most reliable method of mapping drumlins.