Feasibility Study of Mapping Continuous Water Planes Along the Southeast Lake Agassiz Basin

Abstract

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Numerous researchers have reconstructed water planes of glacial Lake Agassiz by mapping discontinuous strandlines throughout the basin. Here we use a detailed, systematic approach using large-scale topographic maps, satellite imagery from Google Earth, and 1/3 arcsecond digital elevation models to map water planes in the southeastern basin of Minnesota from 46°30′ to 48°15′ N latitude along a ~240 km transect between 298–335 m (980–1100 ft) elevation. The intent is to map strandlines, assigning water planes to them and determine if the previously mapped and named strandlines from further south could be mapped northward. To limit bias, the mapping was conducted without prior knowledge of the elevations or locations of the named strandlines (Campbell, Tintah, Upham, Norcross, and Herman). Water planes were identified from escarpments, bars, ridges, spits, and locally, gravel pits and forested regions. Elevation assignments were made to the nearest contour interval (5 or 10 ft) for each apparent water plane assigned to each 7.5′ topographic sheet. Seven water planes emerged from this study site, with four of them traced to the towns for which they are named, and two new strandlines were observed branching to the north. The results show that for the study area it is feasible to extend water planes a significant distance across the Lake Agassiz basin with confidence.