RELATIONSHIP OF DEEP TROUGHS IN THE EASTERN LAKE SUPERIOR BASIN AND LARGE-SCALE GLACIOFLUVIAL LANDFORMS IN THE CENTRAL UPPER PENINSULA OF MICHIGAN

Glaciofluvial landforms of the central Upper Peninsula of Michigan indicate that large discharge events occurred in the late Pleistocene. The approximately 2000-sq-km feature generally known as the Kingston Outwash Plain is a large fan complex that slopes southward from the Lake Superior shoreline between Munising and the Grand Sable Dunes and extends across the Upper Peninsula nearly to Lake Michigan. The head of the outwash plains approximately parallel the modern shoreline along the Munising moraine.

The position and trend of this system of coalescing outwash fans are spatially correlative with deep trenches incised into the floor of Lake Superior. The trenches vary in size but most are 10’s of km in length, several km wide, and up to 700 m deep. The generally south-trending trenches include the deepest spot in the lake. In the past, it was suggested that the trenches terminated abruptly at a bedrock rise about 15 kilometers offshore in Lake Superior. However, the Kingston Lake kettle chain appears to be a partly buried valley that is aligned with one of the main offshore trenches. A 60-m-deep bedrock valley near Miners’ Castle also appears to be an extension of a trench and is at the proximal end of the fan complex.

Bathymetric data, a Digital Elevation Model (DEM) and Landsat Thematic Map images were combined to study the spatial correlation between surface landforms and trenches on the floor of Lake Superior. It is clear that the features on land relate to the moraine formed during the Marquette stadial by the continuity of the landforms. We propose that large-scale subglacial discharge about 10,000 years B.P. facilitated the advance of the Superior lobe to this position and was discharged though the trench system to form the massive fans on the Upper Peninsula. The subglacial meltwater had to be driven up the opposing slope of the Superior basin by the ice-surface slope. An ice surface slope of approximately 11 times the opposing bedrock slope is required to drive water out of pressurized tunnels if subglacial water pressure was close to the flotation point. If the system has lower subglacial water pressure, lesser ice-surface slopes are necessary (W.S.B Paterson, 1998, p. 114).

W.S.B. Paterson, 1998, The Physics of Glaciers, Third Edition. Butterworth-Heinemann, Oxford, England. 480 pp.