Origin and
Evolution of the Great Lakes
Grahame Larson and Randall Schaetzl
This paper presents a synthesis of
traditional and recently published work regarding the origin and evolution of
the Great Lakes. It differs from
previously published reviews by focusing on three topics critical to the
development of the Great Lakes: the
glaciation of the Great Lakes watershed during the late Cenozoic, the evolution
of the Great Lakes since the last glacial maximum, and the record of lake
levels and coastal erosion in modern times.
The Great Lakes are a product of
glacial scour and were partially or totally covered by glacier ice at least six
times since 0.78 Ma. During retreat of
the last ice sheet large proglacial lakes developed in the Great Lakes watershed. Their levels and areas varied considerably
as the oscillating ice margin opened and closed outlets at differing elevations
and locations; they were also significantly affected by channel downcutting,
crustal rebound, and catastrophic inflows from other large glacial lakes.
Today, lake level changes of about a 1/3 m annually, and up to 2 m over 10 to 20 year time periods, are mainly climatically-driven. Various engineering words provide small control on lake levels for some but not all the Great Lakes. Although not as pronounced as former changes, these subtle variations in lake level have had a significant effect on shoreline erosion, which is often a major concern of coastal residents.