The Great Lakes Region
Randall J. Schaetzl
Scott A. Isard
The physical geography of the Great Lakes region is extremely diverse. The region lies on a continental interior plain, halfway between the equator and the North Pole, and as such is located within a latitudinal zone of steep climate and vegetation gradients. Yet five large lakes, for which the region is named, dramatically impact the landscapes in their vicinity. The strong influence that these lakes have on the physical geography, otherwise dominated by dramatic north–south environmental gradients, gives the Great Lakes region its unique and recognized character within North America (fig. 16.1).
The Great Lakes region spans the border of the United States and Canada and is centered on five, geologically young, freshwater lakes: Superior, Michigan, Huron, Erie, and Ontario. Together, they are referred to as the Laurentian Great Lakes and constitute the largest, fresh surface water system on Earth, with an area of 244,160 km2 (Botts and Krushelnicki, 1988) and 20% of the world's fresh surface water (Quinn, 1988; table 16.1). Because large quantities of heat and moisture are transferred to overlying air masses, the Great Lakes strongly influence the climate, and consequently the vegetation, of the region. The region's physical character is rendered even more complex by a geologic transition from the crystalline rocks of the continental craton, overlain by thin glacial sediments, in the north to a series of sedimentary rock strata covered by deep unconsolidated deposits in the south.
The region stands alone as one united by hydrology, and it forms a major environmental ecotone between the intensively used lands to the south and west, with their large urban centers and vast agricultural tracts, and the seemingly endless forests and pristine waterways to the north. This chapter is designed to systematically review the major aspects of the physical geography of the Great Lakes region, with reference to both classical and modern scientific literature.
The Great Lakes region is, with rare exceptions, an area of low irregular plains or plains with hills (fig. 16.2). Lakes, rivers, wetlands, and fresh water abound under a climate that provides enough rainfall and snowfall to support hundreds of perennial streams. The southern part of the region, the Central Lowland province (Hunt, 1967), tends to have low relief and is more or less blanketed with glacial and aeolian sediments (Chapman and Putnam, 1984). In this province, the main relief features are occasional morainal ridges and isolated hills, also of glacial origin, as valley