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Describing the Great Lakes

The Great Lakes comprise the largest chain of connecting, freshwater, inland seas on the planet. They contain more than one-fifth of the world’s surface fresh water. Known also as the Laurentian Great Lakes, they cover a total area of 94,250 sq. miles and their combined low water volume is 5,439 cu. miles. Beaver Island, Isle Royale and Madeline Island are three of 35,000 islands found on the lakes. These lakes have characteristics common to large bodies of water and offer numerous challenges to the maritime industry.

Grant Park and Chicago Harbor
Photo by Elaine C. Shigley

After the last glacial period 10,000 years ago, receding ice sheets carved out deep depressions which filled with the flowing water. Five major lakes—Lake Superior, Michigan, Huron, Erie and Ontario—and numerous minor lakes resulted. These five massive lakes are fresh water seas having undulating tides, persistent airstreams, strong undercurrents, profound depths and unclear distances. In spite of the difficulties, they were used cautiously for transportation and trade by local people who first settled the region.

Lake Superior is the largest by area (31,700 sq. mi. or 82,000 km²) and the world’s largest continental lake. It’s elevated 600 ft. (182.9 m.) above sea level, the highest elevation of the five. Its water volume is the greatest at 2,900 sq. mi. or 12,000 km³. Its deepest level is 1,335 ft. (407 m.) and the average depth is 483 ft. (147 m.). Lake Superior lies in the U.S. and Canada. Duluth, Sault Ste. Marie and Superior are settlements in the U.S. Thunder Bay and Sault Ste. Marie are settlements in Ontario, Canada.

Lake Michigan is the only one of the Great Lakes entirely within the U.S. It covers an area of 22,300 sq. mi. (58,000 km²). At 577 ft. (176 m.), its elevation is only three feet below Lake Superior. To be continued…

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