P1: GIM TJ1095-03 TJ-AEM.cls May 27, 2004 9:29 Morphometric factors in the formation of Great Lakes coastal wetlands C. E. Herdendorf Department of Geological Sciences, The Ohio State University, Columbus, Ohio 43210, USA; E-mail:
[email protected] The Great Lakes basins were carved from ancient river valleys by continental ice sheets that receded from the region less than 10,000 years ago. Not only did the glaciers create the basins now holding the lakes, but they are responsible for many of the shallow depressions in the coastal margin that have since developed as coastal wetlands of various types. For the past four thousand years, coastal processes in the lakes have further modified the shore topography to form embayments, coastal lagoons, estuaries, deltas, and solution basins where thousands of hectares of wetlands have become established. This paper will explore the origin of the various morphometric forms which these wetlands have taken and their characteristic hydrologic processes. Keywords: estuaries, geomorphology, karst, lacustrine, palustrine, physiography Physiography of the Great Lakes gin of the waning ice sheet retreated northward into the newly carved lake basins, some of which were dammed The five adjoining Laurentian Great Lakes— by glacial end moraines. The early ice-margin lakes ex- Superior, Michigan, Huron, Erie, and Ontario—extend panded as the glacial ice masses shrank. However, as 1,370 km from westernmost point to easternmost point new and lower outlets were uncovered to the north, the and 1,130 km from north to south (Figure 1). With lakes drained to ever lowering levels except during peri- a total surface area of 244,160 km2, this is the largest ods of minor readvances of the ice front (Hough, 1962).