GROUND PENETRATING RADAR OF BAY MILLS POINT: STRATIGRAPHIC ARCHITECTURE AND BASE STRUCTURE

This study examines the facies and underlying structures of a natural sand spit in Waiska Bay, Michigan using ground penetrating radar (GPR). The sand spit that forms Bay Mills Point is where Lake Superior enters the St. Mary's River. The spit is exposed to wind and wave action from several directions, it was home to the Hull and Munson Lumber company sawmill until it burned down in 1904. The spit is currently owned by both private land owners and the Army Corps of Engineers.

Seasonal patterns of wave action and longshore currents, winter ice, and water level fluctuations all affect the shape and evolution of Lake Superior's shorelines. Bay Mills Point, however, has remained through recent history. It is hypothesized that sawmill and railroad remains are preserved in the deeper strata contributing to the stability of the base structure (below six meters depth).

These and other industrial remains may be visible in the dataset. Four 250 megahertz transects were acquired in the fall of 2018. Transect 1 extends 180 meters from the tip of the spit inland, crossing an active dune field roughly perpendicular to the dune crests. Transects 2, 3, and 4 intersect transect 1 orthogonally and are oriented sub-parallel to the surface dune ridges. All data were processed with EKKO-Project 4 software and include topographic adjustments, AGC gain and Dewow filter. Deep reflectors (down to eight meters) are indicative of previous sand points that have been buried by subsequent point migration and aggradation.

Continuing analyses will aim to identify dune and shoreline migration patterns, spit growth signatures and any (semi)stable substrates. This will build a sedimentologic and geomorphic model that can provide an analog for the evolution of other Great Lakes mobile shorelines.