BURIED VALLEY MAPPING IN MICHIGAN: A VIEW FROM ONE OF DR. ALAN KEHEW’S LAST GRADUATE STUDENTS

Dr. Alan Kehew (Al) was my advisor, professor, and mentor from 2017 to 2019 during my graduate studies at Western Michigan University (WMU). Upon entering graduate school, my research goals involved geomorphology and near-surface geophysics. It happened that one of the foremost, classical, glacial geologists teaching in the Midwest was seeking students with similar interests. With technical and monetary support from my other WMU committee members (Dr. William Sauck and Dr. Robb Gillespie) and the Michigan Geological Survey (John Yellich), a project evolved to build upon Al’s efforts in techniques to identify buried valleys and testing methods to use in mapping the buried bedrock surface to improve understanding of glacial geology of southwestern Michigan, USA. The graduate project involved using various geophysical methods to estimate bedrock depths below sedimentary cover and to infer previously unknown features in two adjacent topographic quadrangles (Climax & East Leroy) in Michigan. Although most of the Quaternary history of the area was previously described by Al and others, the thickness of the glacial materials and the bedrock surface was not thoroughly mapped. The Horizontal-to-Vertical Spectral Ratio (HVSR) technique was used extensively, along with vertical resistivity soundings, active seismic refraction/reflection surveys, boreholes, and industry seismic data, to better understand the subsurface. This study resulted in the discovery of several bedrock lows interpreted to be bedrock valleys or tunnel valleys. Additionally, identified bedrock highs correspond to terminal ice margins and have some control over post-glacial drainage systems. My funded work was a small contribution to Al’s career of mapping the glacial geology of Michigan. Amongst discussion of my thesis, I will share brief anecdotes about my experiences with Al during graduate school involving mentoring, field trips and field work, and how he prepared me for future geological survey projects.