Articles | Volume 4, issue 4
Earth Surf. Dynam., 4, 831–869, 2016

Special issue: Frontiers in geomorphometry

Earth Surf. Dynam., 4, 831–869, 2016

Research article 08 Nov 2016

Research article | 08 Nov 2016

Reconstruction of North American drainage basins and river discharge since the Last Glacial Maximum

Andrew D. Wickert Andrew D. Wickert
  • Department of Earth Sciences and Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN, USA

Abstract. Over the last glacial cycle, ice sheets and the resultant glacial isostatic adjustment (GIA) rearranged river systems. As these riverine threads that tied the ice sheets to the sea were stretched, severed, and restructured, they also shrank and swelled with the pulse of meltwater inputs and time-varying drainage basin areas, and sometimes delivered enough meltwater to the oceans in the right places to influence global climate. Here I present a general method to compute past river flow paths, drainage basin geometries, and river discharges, by combining models of past ice sheets, glacial isostatic adjustment, and climate. The result is a time series of synthetic paleohydrographs and drainage basin maps from the Last Glacial Maximum to present for nine major drainage basins – the Mississippi, Rio Grande, Colorado, Columbia, Mackenzie, Hudson Bay, Saint Lawrence, Hudson, and Susquehanna/Chesapeake Bay. These are based on five published reconstructions of the North American ice sheets. I compare these maps with drainage reconstructions and discharge histories based on a review of observational evidence, including river deposits and terraces, isotopic records, mineral provenance markers, glacial moraine histories, and evidence of ice stream and tunnel valley flow directions. The sharp boundaries of the reconstructed past drainage basins complement the flexurally smoothed GIA signal that is more often used to validate ice-sheet reconstructions, and provide a complementary framework to reduce nonuniqueness in model reconstructions of the North American ice-sheet complex.

Short summary
The ice sheets that once spread across northern North America dramatically changed the drainage basin areas and discharges of rivers across the continent. As these ice sheets retreated, starting around 19 500 years ago, they sent meltwater to the oceans, influencing climate and building a geologic record of deglaciation. This record can be used to evaluate ice-sheet reconstructions and build an improved history and understanding of past ice-sheet collapse across North America.