In August 2021, the U.S. Geological Survey, in collaboration with the U.S. Army Corps of Engineers, collected high-resolution geophysical data, sediment samples, and bottom imagery to determine the distribution of historical mine tailings on the floor of Lake Superior. Large amounts of waste material from copper mining, locally known as “stamp sands,” were dumped into the lake in the early 20th century, with wide-reaching consequences that have continued into the present. Mapping was focused offshore of the town of Gay on the Keweenaw Peninsula of Michigan, where ongoing erosion and re-deposition of the stamp sands has buried miles of native, white-sand beaches. Stamp sands are also encroaching onto Buffalo Reef, a large area of cobble/boulder substrate that supports productive fisheries in the lake.
The objectives of this cooperative mapping project are to develop a framework for scientific research and provide baseline information required for management of resources within the coastal zone of northern Michigan. High-resolution bathymetry and backscatter data reveal the irregular topography of the shallow, cobble-covered Buffalo Reef and the relatively smooth surface of finer-grained sediment that covers adjacent, deeper parts of the lake floor. Previous research used numerous sediment samples to determine the general distribution of mine tailings on the lake floor in this area, but little information exists on the extent and thickness of the surficial deposits. The main priority of this project is to image the near-surface stratigraphy, specifically the thickness of surficial sand and mud that threaten to cover the reef, with seismic-reflection profiling systems. In addition to continuous coverage of bathymetric and backscatter data, this project collected a dense grid of closely spaced seismic profiles in 2018, which will guide efforts to mitigate the environmental impacts of the shifting stamp sands. This 2021 (2021-005-FA) survey is the second survey conducted by the Woods Hole Coastal and Marine Science Center (WHCMSC) in Grand Traverse Bay, Houghton County MI. The first survey conducted in September 2018 (2018-043-FA) was a regional geologic framework study that covered a large area (30 sq km) and lower resolution (2-m) and included both single-channel, and swept frequency (chirp) subbottom seismic profiles. Data from this survey were published in Andrews and other (2020), see cross-reference section below for details. The data from the 2018 survey was used to plan the higher resolution (less than 1-m) 2021 survey that covered a smaller area (14 sq km) focused on Buffalo Reef and included 410 bottom photographs, and 60 sediment samples collected using the MiniSEABOSS.