VISUALIZING HOLOCENE LANDSCAPES: ISOSTATIC REBOUND AND LAKE LEVEL VARIATIONS IN THE SUPERIOR BASIN

The Lake Superior region has undergone dramatic environmental changes throughout the Quaternary Period. The effects of these changes on the landsurface, such as fluctuating lake level, can be subtracted from modern topography to create paleo-landscape surfaces. In order to model Lake Superior's past landscape, the effects of both variable lake level and isostatic rebound must be removed. The large lakes that have occupied the Superior Basin for most of the Holocene left paleo-shorelines as markers of the elevation of their water surfaces. As glaciers receded from the basin, 12- 10 ka, new lower outlets were uncovered causing drops in absolute lake level. Lake levels increased from the Houghton Lowstand, 9,000 BP till the Nipissing Highstand, 5,500 BP. A brief interval of falling lake levels ended approximately 2,200 BP as Lake Superior reached the Sault outlet, the lowest in the basin. Continued uplift of the Sault due to isostatic rebound has caused subsequent rise in the level of Lake Superior. Rebound rates have been calculated for the basin using a combination of paleo-shoreline elevations and calculations from water gauging stations around Lake Superior. Using a geographic information system (GIS), paleo-landscapes of the Superior Basin can be created. A 3 arc second DEM of the Lake Superior Basin is used as a base map. This surface is incrementally corrected for rebound at 500 yr intervals back to 9,500 years ago to reconstruct the paleo-topography. These paleo-topographic surfaces can then be combined with lake level data to create a comprehensive view of the Superior Basin throughout the Holocene.