Pre-Illinoian glacial geomorphology and dynamics in the central United States, west of the Mississippi

James S. Aber

Earth Science, Emporia State University, Emporia, KS 66801, aberjame@emporia.edu

A GIS database has been compiled for pre-Illinoian glacial margins and related melt-water drainage features in the region west of the Mississippi. The GIS database was assembled from various published and unpublished sources; it includes glacial margins of different ages, melt-water channels, preglacial (buried) valleys, preglacial drainage divides, and related features, which are portrayed on a background constructed from a digital elevation model.

From this database, several observations have emerged. 1. Many more ice-margin positions are mapped than ever described before, especially in eastern Nebraska and southern Iowa. 2. Melt-water drainage valleys are well preserved in bedrock and represent the most important long-term geomorphic legacy of glaciation. 3. Melt-water drainage routes are situated in two positions--parallel and normal to ice margins. The parallel routes are arranged in concentric, nested patterns that mark positions of glacier advance and retreat. The normal routes are either parallel or slightly diverging in the downstream direction. These drainage routes, at right angles to ice margins, presumably formed as either subglacial tunnel valleys or proglacial spillways, in places following preglacial valleys. They probably served repeatedly in both roles during multiple glacier advances and retreats. The overall pattern of ice margins and drainage routes strongly suggests a lobate style for pre-Illinoian glaciations, in which ice-lobe surging may have taken place.

Taken from: Aber, J.S. 1999. Pre-Illinoian glacial geomorphology and dynamics in the central United States, west of the Mississippi. Geological Society of America, Special Paper 337, p. 113-119.

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