Outburst flood origin of the Central Kalamazoo River Valley, Michigan, USA

Abstract

Geomorphic evidence and stratigraphic information from boreholes suggest that the oversized Central Kalamazoo River Valley (CKRV) in southwest Michigan resulted from a catastrophic outburst flood emanating from subglacial channels under the Saginaw lobe of the Laurentide Ice Sheet. The CKRV occurs as a deeply incised trench over 2 km wide and in excess of 50 m deep situated in a reentrant formed by the Lake Michigan, Saginaw and Huron-Erie lobes. The course of the CKRV follows an irregular flow path that bisects the Kalamazoo Moraine of the Lake Michigan lobe. Erosional terraces near the mouth of the channel indicate that Lake Michigan lobe meltwater drained eastward prior to the westward Saginaw outburst. Prior to valley formation the Lake Michigan lobe had retreated westward to at least the Lake Border Moraine. With the Lake Michigan lobe absent to impede flow, drainage from the CKRV proceeded southwesterly until draining into glacial Lake Chicago near St. Joseph, Michigan. The outburst originated from a system of Saginaw tunnel channels that display convex-up flow profiles and contain eskers. Meltwater drainage transitioned from subglacial-to-ice marginal and proglacial environments. During the interval represented by the outburst, the Saginaw Lobe appears to have been in a relatively stationary position.