Reserve Mining Tailing Fan
Reserve Mining, currently Northshore Mining, dumped their waste rock, or tailings, into Lake Superior during the 50's, 60's and 70's. Researchers from the Large Lakes Observatory have used a multibeam sonar, mounted on the bottom of the University's research vessel, the Blue Heron, to map the extent of the subaqueous fan of tailings on the lake floor.
The area mapped was 7 by 7 km off of Silver Bay, MN, ranging from 20 to 285 meters of water depth. The multibeam data have a horizontal resolution of 5 meters at the maximum depth. The data have been converted into the faux three dimensional images on this page. The image to the right is a view of the multibeam survey area as you look north. The image depicts the lake bottom from shallow waters (20 meters) in the upper part of the image to deep waters (280 meters) in the bottom part of the image. Since the image is 7 by 7 km in extent, there is a large vertical exaggeration (10X).
Below are two images illustrating the multibeam data as one looks to the southeast, or down slope, from shore to deeper waters. Taconite tailings fill in low spots, essentially smoothing the lake bottom. The image on the left gives an indication of the extent of the tailings on the lake bottom.
Below is a chart of western Lake Superior showing the location of the multibeam survey area off of Silver Bay, MN. This is a section of NOAA chart 14967. You can look at more NOAA charts and the User's agreement online.