Mapping the Stamp Sands of Lake Superior

This article is part of the December 2018-January 2019 issue of the Sound Waves newsletter.

Large amounts of waste material, called “stamp sands,” from copper mining were dumped into the lake at many locations in the early 20^th century, with wide-reaching consequences that have continued into the present day. Mapping was focused offshore of the town of Gay on the Keweenaw Peninsula of Michigan where ongoing erosion and re-deposition of the toxic stamp sands has buried miles of native, white-sand beaches. The stamp sands are also steadily encroaching on 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.

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This project is jointly funded by the WHCMSC, USGS Midwest Region, and the Detroit District of the US Army Corps of Engineers (USACE). Modeling studies by the USACE previously concluded that the reef area buried by stamp sands will more than double from 25 percent to 60 percent over the next 10 years if no action is taken (Hayter et al., 2015). Several mitigation options are being examined, including

• construct a stone revetment around the spoils pile,
• remove the spoils pile and dump in deep water,
• excavate an underwater trough to intercept the sands before they reach the reef.

To test potential outcomes under these (and other) scenarios, accurate data on the current distribution of stamp sands and the processes/pathways of sediment transport in the area were needed. Cooperating institutions include Michigan Technical University (MTU) in Houghton, MI, where researchers have conducted research on the environmental legacy of copper mining in the region for many years.

The journey between Woods Hole to northern Michigan is long. Barry Irwin, Alex Nichols and David Foster hauled the R/V Rafael, the Center’s well-equipped 25’ mapping vessel over 1200 miles each way to conduct the survey. The crew, including Walter Barnhardt and Brian Andrews, collected approximately 370 kilometers of geophysical tracklines and collected sediment samples at 17 stations over the course of the two-week survey. Bathymetry and backscatter data from a multibeam echosounder and subbottom data from boomer and chirp seismic-reflection profilers were used to map the geologic framework of approximately 30 square kilometers of the lake in depths of 4–35 meters. These data will be compiled with existing lidar, video, and sample data from MTU to produce geologic maps of the area, with particular focus on the stamp sands. The dense array of subbottom data will guide the selection of cores to be collected by Rachel Malburg (ACOE) in 2019.

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Sources/Usage: Public Domain. View Media Details

Sources/Usage: Public Domain. View Media Details

Although unsalted and shark free, Lake Superior certainly lived up to its reputation as a rugged body of water. For several days, an easterly gale blew, waves built to 10 feet, and the lake waters turned brown with sediment derived from the spoils pile. The stamp sands—dark gray in color with metal-rich geochemical signatures—are readily distinguishable from the region’s native quartz sands and thereby represent an excellent tracer for tracking sediment movement across the submerged landscape. The well-constrained history of emplacement and subsequent erosion of the stamp sands offers a unique opportunity to validate models of sediment supply on coastal evolution since mining ceased in the 1930s. Of the approximately 22.7 million metric tons (37.3 million cubic yards) deposited at the Gay site MTU investigators (Kerfoot et al., 2012) have estimated that more than 85 percent of the original pile of stamp sand has been eroded. Movement of that sediment has caused progradation of the beach and damming of stream outlets downdrift of the pile. In the offshore, USGS mapping will characterize the extent of sedimentation on the sensitive hard-bottom habitats, and help quantify the spreading environmental effects from copper and other metals that threaten critical fish breeding grounds.

References:

Hayter, E., Chapman, R., Lin, L., Luong, P., Mausolf, G.,  Perkey, D., Mark, D., and Gailani., J., 2015, Modeling sediment transport in Grand Traverse Bay, Michigan to determine effectiveness of proposed revetment at reducing transport of stamp sands onto Buffalo Reef: US Army Corps of Engineers, ERDC Letter Report, 71 p.

Kerfoot, W.C., Yousef, F., Green, S.A., Regis, R., Shuchman, R., Brooks, C.N., Sayers, M., Sabol, B., and Graves, M., 2012, LiDAR (Light Detection and Ranging) and multispectral studies of disturbed Lake Superior coastal environments: Limnology and Oceanography, v. 57, p. 749–771, https://doi.org/10.4319/lo.2012.57.3.0749.