|Physical Features of Great Lakes
The Great Lakes are a group of five large freshwater lakes in central North America, interconnected by natural and artificial channels. From west to east they are Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario. Lake Michigan lies entirely within the United States; the others form part of the border between the United States and Canada. The combined surface area of the lakes is 244,100 sq km (94,250 sq mi). Together the lakes drain a total of about 750,000 sq km (about 290,000 sq mi) in Canada and the United States. The primary outlet of the system is the St. Lawrence River; a portion is diverted from Lake Michigan to the Chicago River. The lakes are bordered by the Canadian province of Ontario and by eight U.S. states: New York, Pennsylvania, Ohio, Indiana, Michigan, Illinois, Minnesota, and Wisconsin.
The Great Lakes are a natural resource of tremendous significance in North America, serving as the focus of the industrial heartland of the continent. Together they hold about 20 percent of the world's fresh surface water. Four of the 20 largest cities in North America (Chicago, Detroit, Toronto, and Cleveland) lie on the shores of the Great Lakes system and owe much of their wealth to commerce attracted to the lakes. The lakes also form an important recreational resource with about 17,000 km (about 10,500 mi) of shoreline, rich sport fisheries, and numerous beaches and marinas.
The beaches of the Great Lakes are some of the best in the world and add considerably to the recreational attraction of the state. Inland from the beaches, there are often beautiful sand dunes, a distinctive feature of the topography of Michigan, particularly along the eastern shore of Lake Michigan. Recently, a problem has developed in the level of the water in the western Great Lakes surrounding the state of Michigan. The level fluctuates from 1 to 2 m over a period of years because of the amount of precipitation and runoff received. In the 1970s, a near all-time high of nearly a meter above the mean level was reached by Lakes Huron and Michigan, and considerable lakeshore damage occurred as a result.
Although individual owners as well as certain cities and villages along the shore are developing piers, breakwaters, groins, and seawalls of various kinds to protect the shore, high-water erosion and flood damage still threaten the shoreline. The erosive power of a fall or spring storm on Lake Michigan, Lake Superior, or Lake Huron is awesome. The Army Corps of Engineers is studying the problem of fluctuating lake levels, but there are no easy solutions. One possible remedy is to allow more water to go out through the southern end of Lake Michigan (i.e., be diverted from the basin), via the Chicago River, and on into the Mississippi River. However, it is estimated that this action would have only a minor effect on the problem. Another suggestion has been made that the outlet near the St. Clair and Detroit Rivers--and further, the Niagara River, which is the outlet of Lake Ontario--be lowered so that the volume of water that can flow out through the St. Lawrence River would be increased. This may be more effective solution, but it would take a great deal of coordination between the different states involved, as well as the cooperation of Canada.
Lake Superior, the largest in area of the Great Lakes at 82,100 sq km (31,700 sq mi),
is the largest freshwater lake in the world. Of the Great Lakes, Lake Superior is the
highest above sea level, at 183 m (600 ft), the farthest north, and the coldest. Its
outlet is the Saint Marys River, which enters Lake Huron after falling about 7 m (about 21
ft) over a series of rapids between the twin cities of Sault Sainte Marie, in Ontario and
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