A B C D E The Great Lakes during several eras: (A) 15,400, (B) 13,000, (C) 11,800, and (D) 6,000 years ago, and (E) the present day. Controlling outlets are indicated by red dots and the direction of outflow shown by arrows. Shifting Shorelines Continued from page 25 For more information, contact Kevin Befus is now using shallow surface geophysical methods to characterize the Boulder Creek Critical Zone Observatory while pursuing a master's degree at the University of Colorado in Boulder, Colorado. References Cathles, Lawrence M. (1975), The Viscosity of the Earth's Mantle. Princeton, NJ: Princeton University Press. Dyke, Arthur S. (2004), "An Outline of North American Deglaciation with Emphasis on Central and Northern Canada." In Quaternary Glaciations—Extent and Chronology, Part II, J. Ehlers and P. L. Gibbard, eds. Amsterdam: Elsevier, Developments in Quaternary Science, Vol. 2b, 373–424. Farrell, W. E., and James A. Clark (1976), "On Postglacial Sea Level." Geophysical Journal of the Royal Astronomical Society 46:647–667. Hough, Jack L. (1958), Geology of the Great Lakes. Urbana, IL: University of Illinois Press. Peltier, W. R. (1974), "The Impulse Response of a Maxwell Earth." Reviews of Geophysics and Space Physics 12:649–669. Wu, P., and W. R. Peltier (1983), "Glacial Isostatic Adjustment and the Free Air Gravity Anomaly as a Constraint on Deep Mantle Viscosity." Geophysical Journal of the Royal Astronomical Society 74:377–450. Esri Training An instructor-led course, Working with ArcGIS Spatial Analyst, is offered. Visit www.esri.com/ training for dates and locations. Acknowledgments This work was funded by grants from the National Science Foundation (NSF Grants EAR-0414012 and EAR-0624199), the National Aeronautical and Space Administration (NASA Grant NAG5-10348), Wheaton College, the Wheaton College Alumni Association, and the United States Geological Survey National Cooperative Geologic Mapping Program. Tom Hooyer provided encouragement and insight throughout this work. Steve Colman and Shiyong Yu kindly provided their unpublished Lake Superior bathymetry data. About the Authors James Clark is a professor of geology in the geology and environmental science department at Wheaton College in Wheaton, Illinois. In addition to the Great Lakes studies, his research interests include global sea level changes and water supply problems in developing nations. His Ph.D. is from the University of Colorado. A Greener Choice Complete issues of ArcUser are instantly available online in flipbook or PDF versions. www.esri.com/arcuser 26 ArcUser Summer 2009 www.esri.com