Paleogeographic Maps of Lake Agassiz Miranda Johnson, Environmental Science Major Mentor Dr. Andrew Breckenridge, Department of Natural Sciences Contact: [email protected]

Abstract Results Discussion Lake Agassiz was the largest glacial lake in North America covering parts • The construction of Lake Agassiz topography for nine discrete time of Canada and northern Minnesota. Lake Agassiz had quite the periods provides representations of how Lake Agassiz may have looked significance as it is suggested to have impacted climate as the lake levels 13,500 Years Ago 12,800 Years Ago 12,100 Years Ago and fluctuated over time. fluctuated over time (Stone, J., & Fritz, S.,2013). The purpose of this • The maps suggest that initially glacial Lake Norwood covered the area research is to create maps to see if the Lake Agassiz sediment records in that is now Voyageurs National Park (VNP), around 13,500 years ago the lakes Voyageurs National Park are consecutive. I constructed • Lake Norwood and Agassiz merged, and covered VNP around 12,800 topography maps using current and ongoing studies with the ice margins years ago. of the Laurentide Ice Sheet (Dalton et al.,2020), glacial isostatic • As the ice sheet retreated, the outlet for Lake Agassiz shifted to the adjustment, isobases, modern topography, ancient topography and the northwest around 12,100 years ago. use of ArcGIS. The Lake Agassiz sediment records, according to the maps, Lake Norwood • By 11,500 years ago, Lake Agassiz levels rise and re-flood VNP. in Voyageurs National Park suggest that Lake Agassiz sediments were • Around 10,300 years ago the outlet shifted back down to the nonconsecutive. southeast. • Before 9,600 years ago, a new outlet opens into Lake Superior, and Introduction Agassiz levels fall, and never to return to VNP Lake Agassiz was a large proglacial lake that existed during the end of the last ice age, around 14,000-8,000 years ago (Redekop,2017). The lake 11,800 Years Ago 11,500 Years Ago 11,000 Years Ago Conclusion fronted the Laurentide Ice Sheet, and this ice sheet was used to • The Lake Agassiz sediment records in the lakes of Voyageurs National understand glacial isostatic adjustment. Glacial isostatic adjustment Park were nonconsecutive. The maps suggest that the lake during refers to the return to equilibrium in response to the ice sheet melting. certain time slices did not occupy the region where VNP is now For example, as the ice sheet began to melt the earths crust began to located. rise. Back when the Laurentide Ice Sheet would retreat, the crust below would rise back up and collect sediment deposit (N.O.A.A, 2021). In present day over in Voyageurs National Park sediment records show that References and Acknowledgements Lake Agassiz deposited sediments which are found at the bottom of the • Financial support for this project was provided by the University of park's lakes. Wisconsin-Superior and the TRIO Ronald E. McNair Postbaccalaureate Achievement Program, grant number P217A170017 Research Question • Aaron Wainman • Andrew Breckenridge • Will the Lake Agassiz sediment record in the lakes of Voyageurs Breckenridge, A. (2015). The Tintah-Campbell gap and implications for National Park be consecutive? 10,300 Years Ago 9,600 Years Ago glacial Lake Agassiz drainage during the Younger Dryas cold interval. Quaternary Science Reviews, 117, 124–134. Methods https://doi.org/10.1016/j.quascirev.2015.04.009 Dalton, et al. (2020). An updated radiocarbon-based ice margin • Using GIA to construct ancient topography maps and predict the size chronology for the last deglaciation of the North American Ice Sheet and shape of Lake Agassiz. Complex. Quaternary Science Reviews, 234, 106223. • Used isobase (lines of equally depressed crust) to reconstruct the https://doi.org/10.1016/j.quascirev.2020.106223 depressed crust at each time period (Breckenridge, 2015). Mann, J. D., Leverington, D. W., Rayburn, J., & Teller, J. T. (1999). The volume and paleobathymetry of glacial Lake Agassiz. Journal of • Subtract ancient surfaces from modern surface topography which then Paleolimnology, 22(1), 71–80. became reconstructed elevation models https://doi.org/10.1023/a:1008090015161 • Used Dalton et al (2020) N.O.A.A. (2021a, February 26). What is glacial isostatic adjustment? ice margin National Oceanic and Atmosphere Association. reconstructions to figure Figure 2. https://oceanservice.noaa.gov/facts/glacial-adjustment.html out the geography A series of 9 topography maps of Lake Agassiz. Each map represents approximately where Redekop, Bill. (2017).Lake Agassiz the Rise and Demise of the Associates. • For each time slice, we the lake was located relative to Voyageurs National Park. Redekop, Bill. (2017).Lake Agassiz the Rise and Demise of the World’s found the lowest GreatWorld’s Greatest Lake. Heartland est Lake. Heartland Associates. elevation to construct Stone, J., & Fritz, S. (2013). LAKE LEVEL STUDIES | North America. the lakes outlet and Figure 1. Legend Encyclopedia of Quaternary Science, 537–548. contoured the elevation The lines represent https://doi.org/10.1016/b978-0-444-53643-3.00166-7 all with the help of where the earth's Outlet Thorleifson, L. H. 1996. Review of Lake Agassiz History. in Sedimentology, ArcGIS crust had equal Geomorphology, and History of the central Lake Agassiz Basin, Field depression. Voyageurs National Park Trip B2, Teller, J. T., Thorleifson, L. H., Matile, G., and Brisbin, W. C., (Thorleifson, 1996)) eds., Geological Association of Canada Guidebook, p. 55-84