Submarine Valleys in Lake Superior

Abstract

T HE accelerated increase in the size, draft, and speed of Great Lakes vessels in recent years and the increase in the size and draft of ocean vessels entering the Great Lakes since the opening of the St. Lawrence Seaway have produced a need for improvements in the lake charts, particularly in the detail of the hydrographic features, and have emphasized the importance of the re-sounding program of the United States Lake Survey.' In 1945 the Lake Survey, anticipating the need for improvement of navigation charts because of increases in the draft of vessels on the Great Lakes, began re-sounding the deep-water areas of the lakes where earlier sounding had provided only a superficial idea of the configuration of the bottoms. Before 1945 the deep-water areas had been sounded on lines about three miles apart. The re-sounding program contemplated lines of soundings no more than one and one-half miles apart, and spaced more closely where indications were obtained that shoaler waters might exist between the one and one-half mile lines. The soundings, analyzed by trained hydrographers as the survey progressed, were expected either to disclose uncharted shoals that will be hazardous to the larger and swifter vessels evolving on the lakes or to establish that such shoals do not exist.