Submersible Studies of Current-Modified Bottom Topography in Lake Superior

• Published in: Journal of Great Lakes research 1989, Vol.15 (1), p.3-14
• Main Author: Flood, Roger D.
• Format: Article
• Language: English
• Subjects: arcuate depressions; bedforms; bottom sediments; currents; Freshwater; rings; side-scan sonar; sonar; submarines; Underwater
• ISSN: 0380-1330
• DOI: 10.1016/S0380-1330(89)71457-X

Submersible studies of deep-lake sedimentary features, especially furrows (at 100 m water depth) and large arcuate depressions (at 240 m water depth), in an area directly north of the Keweenaw Peninsula, Lake Superior, have shown that currents deep in the lake are important agents in depositing and eroding sediments and in creating surficial sediment variability. Furrows are linear, parallel troughs created by flow-sediment interactions, and these bedforms are commonly observed in estuaries and in the deep sea. Sedimentological and isotopic studies show that sediment accumulation rates vary by 60% to 80% across the furrow profile (lower accumulation rates in the trough). Also, strong currents (to 28.5 cm/sec at 10 m above the bottom) sweep the bottom at 100 m water depth during the fall, winter, and spring when the lake is poorly stratified. These currents are strong enough to erode the furrowed sediments. Large arcuate depressions (about 5 m deep, 50 m wide, and 300 m long) are eroded into varved, carbonate-rich gray glacial clays in the deep lake floor. Ripples, developed on the trough walls, suggest that deep currents are occasionally strong enough to rework sediments at 240 m. Also, carbonate in the varved gray clays exposed on the walls and floor of the depressions may be dissolved by the undersaturated lake waters, leading to enhanced erosion. Both furrows and arcuate depressions have been observed in other Great Lakes.