The volume and paleobathymetry of glacial Lake Agassiz

During the last retreat of the Laurentide Ice Sheet in North America, many proglacial lakes formed as continental drainage was impounded against the s outhern and western ice margin. Lake Agassiz was the largest of these lakes . The bathymetry of Lake Agassiz at the Herman and Upper Campbell beach lev els - formed at about 11.5-11.0 ka and 9.9-9.5 ka, respectively - was compu ter modelled in this study by first collecting data for the isostatically-d eformed paleowater planes of the two lake levels (derived from isobase line s constructed from beach elevations), and then subtracting these from the m odern topography of the former lake floor. Pixels with dimensions of 1/30 X 1/30 of a degree were used in the model. Using these data, the area and vo lume of the lake were also calculated: at the Herman level these were simil ar to 152 500 km(2) and similar to 13 100 km(3) respectively; at the Upper Campbell level these were similar to 350 400 km(2) and similar to 38 700 km (3). Contour maps showing the paleobathymetry of both periods in the lake's history were also constructed. Determining the paleobathymetry and volume of Lake Agassiz is an important step in understanding the impact that the l ake had on its surrounding environment and on the rivers, lakes, and oceans into which it flowed.