Side‐scan targets in Lake Superior—evidence for bedforms and sediment transport

Abstract

A high‐resolution side‐scan sonar survey of the lake bed off the Keweenaw Peninsula, Lake Superior, demonstrates that bottom currents are affecting lake bed morphology at depths up to 240 m. Numerous lineations which run parallel to the shore appear to be sand ribbons. A field of sedimentary furrows which occurs in one area demonstrates the long‐term directional stability of the near‐bottom flow. Large (100–300 m in diameter, 2–5 m deep), unusual ring‐like or arcuate depressions are common throughout the western half of Lake Superior. These rings themselves do not appear to have been formed by bottom currents, but may have developed as water was released by the rapid compaction of glacial sediments which underlie the lake bed. Off the Keweenaw Peninsula the forms of the rings have been modified by bottom currents. The bottom currents which have modified the lake bed are probably generated when storms cross the lake at times when it is poorly stratified.

Radiocarbon and stable‐isotope geochemistry of organic and inorganic carbon in Lake Superior

“…Similarly, using a submersible equipped with video, camera, and a sampler, Flood [1989]reported large arcuate depressions at 240 m and furrows at 90 m water depth sites in the central basins, consistent with observations from side‐scan sonar [ Flood and Johnson , 1984], and caused by extensive erosion and resuspension of sediments. Furthermore, Hawley [2000] also reported sedimentary resuspension and transport offshore in a study off the Keweenaw Peninsula.…”

Recognition of an early Holocene polygonal fault system in Lake Superior: Implications for the compaction of fine-grained sediments

“…Based on this correspondence, we consider that this newly identified Lake Superior pockmark field extends regionally to encompass the area represented by the irregular lake-floor topography, characterized mainly by lakefloor depressions a few meters in depth; the field covers the large region of the western part of the lake, as shown in Figure 1C. Although the lake-floor depressions have been recognized in previous studies (referred to as ''rings'') and have been linked to dewatering processes (Flood and Johnson, 1984), they have not previously been dated accurately, nor have they been mapped either regionally or in detail, and their likely origin as pockmarks has therefore not been appreciated before now.…”

A high resolution study of spatial and temporal variability of natural and anthropogenic compounds in offshore Lake Superior sediments

“…1). While these features have been known for some time (e.g., Berkson and Clay, 1973;Flood, 1989;Flood and Johnson, 1984;Johnson et al, 1984), their ubiquitous presence on the lake floor, their morphology, and their impact on sediment accumulation more recently have been imaged clearly through the use of multi-beam sonar combined with digital, single-channel, highresolution seismic-reflection profiling (Cartwright et al, 2004). The depressions are associated with a polygonal system of faults in the underlying glacial-lacustrine clays, and are attributed to dewatering of the clays since their deposition between 9000 and 10,600 years ago (Cartwright et al, 2004).…”