Multibeam backscatter data collected in the vicinity of Buffalo Reef, Michigan, within Lake Superior during USGS Field Activity 2021-005-FA using a dual-head Reson T20-P multibeam echosounder (8-bit GeoTIFF, UTM Zone 16N, NAD 83, 1-m resolution)

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.

2021年8月，美国地质调查局（U.S. Geological Survey）与美国陆军工程兵团（U.S. Army Corps of Engineers）合作，采集了高分辨率地球物理数据、沉积物样品与海底影像，以确定苏必利尔湖湖床历史矿尾矿的分布情况。20世纪早期，大量铜开采产生的废弃物（当地称为“磨矿砂（stamp sands）”）被倾倒入湖，其影响范围广泛且持续至今。测绘工作聚焦于密歇根州基威诺半岛盖伊镇近岸海域——该区域磨矿砂持续侵蚀与再沉积，已掩埋了数英里原生白沙滩。此外，磨矿砂还正侵入布法罗礁（Buffalo Reef），这片以砾石/巨砾为基底的大型区域支撑着湖内高产渔业。
本合作测绘项目的目标是构建科学研究框架，并为密歇根州北部海岸带的资源管理提供所需的基线信息。高分辨率水深与反向散射数据揭示了浅水区覆有砾石的布法罗礁不规则地形，以及覆盖湖床相邻较深区域的细粒沉积物相对平滑的表面。此前的研究通过大量沉积物样品确定了该区域湖床矿尾矿的大致分布，但关于表层沉积物的范围与厚度的信息却十分有限。本项目的核心优先级是利用地震反射剖面系统对近地表地层进行成像，重点是可能覆盖该礁体的表层砂与泥的厚度。除了获取全覆盖的水深与反向散射数据外，本项目还于2018年采集了密集网格的近距离地震剖面，这将为缓解移动磨矿砂带来的环境影响提供指导。
本次2021年（项目编号2021-005-FA）调查是伍兹霍尔海岸与海洋科学中心（Woods Hole Coastal and Marine Science Center, WHCMSC）在密歇根州霍顿县大特拉弗斯湾开展的第二次调查。2018年9月开展的首次调查（项目编号2018-043-FA）为区域地质框架研究，覆盖面积达30平方千米，分辨率较低（2米），包含单通道与扫频（chirp）浅地层地震剖面。该调查的数据已发表于Andrews等人（2020），详细信息参见下文交叉参考部分。2018年调查所获数据被用于规划本次分辨率优于1米的2021年高分辨率调查：本次调查覆盖面积缩小至14平方千米，聚焦布法罗礁，共采集了410张海底照片与60份通过MiniSEABOSS获取的沉积物样品。