Lake Michigan, the only one of the great lakes of North America wholly within the boundaries of the United States, and the second largest body of fresh water in the world. It lies S. of Lake Superior and W. of Lake Huron, between 41° 37' and 46° 05' N. and 84° 45' and 88° W.; is bounded on the N. and E. by the state of Michigan, on the W. by Wisconsin, while Illinois and Indiana touch its S. end. It is 320 m. long, and has an average width of 65 m. The maximum depth recorded by the United States Lake Survey is 870 ft.; the mean level of the surface is 581.3 ft. above mean sea-level, being the same as that of Lake Huron and 21 ft. below that of Lake Superior. Its area is 22,400 sq. m., and it has a basin 68,100 sq. m. in area.
The shores of Lake Michigan are generally low and sandy, and the land slopes gradually to the water. The northern shore of the lake is irregular and more rugged and picturesque than the other shores, the summit of the highest peak being about 1400 ft. above the sea. On the eastern side are numerous sand hills, formed by the wind into innumerable fantastic shapes, sometimes covered with stunted trees and scanty vegetation, but usually bare and rising to heights of from 150 to 250 ft. The south-western shore is generally low, with sand hills covered with shrivelled pines and bur oaks. Along the western shore woods and prairies alternate, interspersed with a few high peaks. The cliffs on the east shore of Green Bay form a bold escarpment, and from this ridge the land slopes gradually to the lake. With the exception of Green and Traverse bays, Lake Michigan has few indentations of the coast line, and except at the north end it is free from islands. The waters near shore are shoal, and as there are few harbours of refuge of easy access navigation is dangerous in heavy storms. Around the lake the climate is equable, for, though the winter is cold and the summer hot, the waters of the lake modify the extremes, the mean temperature varying from 40° to 54° F. The average annual rainfall is 33 in. The finest agricultural land in the United States is near the lake, and there is an immense trade in all grains, fruits, livestock and lumber, and in products such as flour, pork, hides, leather goods, furniture, &c. Rich lead and copper mines abound, as also salt, iron and coal. Abundant water power promotes manufactures of all kinds. Beer and distilled liquors are largely manufactured, and fine building stone is obtained from numerous quarries.
The lake is practically tideless, though true tidal pulsations amounting to 3 in. in height are stated to have been observed in Chicago. In the water of the lake there is a general set of current towards the outlet at the strait of Mackinac, following the east shore, with slight circular currents in the main portion of the lake and at the northern end around Beaver island. These currents vary in speed from 4 to so m. per day. Surface currents are set up by prevailing winds, which also seriously affect water levels, lowering the water at Chicago and raising it at the strait, or the reverse, so as greatly to inconvenience navigation. The level of the lake is subject to seasonal fluctuations, reaching a maximum in midsummer and a minimum in February, as well as to alternating cycles of years of high and low water. Standard highwater of 1838 was 3.36 ft. above mean level and standard low-water of 1895, 2.82 ft. below that datum, giving an extreme recorded range slightly over 6 ft.
The northern portion of the lake only is covered with ice in winter, and ice never reaches as far south as Milwaukee. Milwaukee River remains closed on an average for one hundred days - from the beginning of December to the middle of March. The average date of the opening and closing of navigation at the strait of Mackinac, where the ice remains longest, is the 17th of April and the 9th of January respectively.' Regular lines 'of steamers specially equipped to meet winter conditions, most of them being car ferries, cross the lake and the strait of Mackinac all winter between the various ports.
No notable rivers flow into Lake Michigan, the largest being the Big Manistee and Muskegon on the east shore, and on the west shore the Menominee and the Fox, both of which empty into Green Bay, the most important arm of the lake. The numerous harbours are chiefly artificial, usually located at the mouths of streams, the improvements consisting of two parallel piers extending into the lake and protecting a dredged channel. Sand bars keep filling up the mouths of these channels, necessitating frequent dredging and extension of the breakwaters, work undertaken by the Federal government, which also maintains a most comprehensive and completeystem of aids to navigation, including lighthouses and lightships, fog alarms, gas and other buoys, life-saving, storm signal and weather report stations.
1 Report of Deep Waterways Commission (1896).
Chicago, the principal port on the lake, is at its south-west extremity, and is remarkable for the volume of its trade, the number of vessels arriving and departing exceeding that of any port in the United States, though the tonnage is less than that of New York. It is a large railway centre, and the number and size of the grain elevators are noticeable. The port is protected by breakwaters enclosing a portion of the lake front. The level of the city above the lake being only 14 ft., much difficulty arose in draining it. A sanitary and ship canal 34 m. long was therefore completed in 1900 to divert the Chicago river, a small stream that flows into the lake, into the head waters of the Des Plaines river and thence through the river Joliet into the Mississippi at St Louis. The discharge of water is by law so regulated that the maximum flow shall not exceed 250,000 cub. ft. per minute. The effect upon the permanent level of the lakes of the withdrawal of water through this artificial outlet is receiving much attention. Milwaukee, situated on the shore of Milwaukee Bay, on the western side of the lake, is, next to Chicago, the largest city on the lake, and has a large commerce and a harbour of refuge. Escanaba, on Little Bay de Noc (Noquette), in the northern part of the lake, is a natural harbour and a large iron shipping port. Green Bay and Lake Michigan are connected by a canal extending from the lake to the head of Sturgeon Bay. Lake Michigan is connected at its north-east extremity with lake Huron by the strait of Mackinac, 48 m. long, with a minimum width of 6 m.; the water is generally deep and the shoals lying near the usually travelled routes are well marked.
BIBLIOGRAPHY
Sailing directions for Lake Michigan, Green Bay, and the Strait of Mackinac, U.S. Navy Hydrographic office publication No. 108 B (Washington, 1906); Bulletin No. 17: Survey of Northern and North-western Lakes, U.S. Lake Survey Office (Detroit, Michigan, 1907); St Lawrence Pilot, 7th ed., Hydrographic Office Admiralty (London, 1906); Effect of Withdrawal of Water from Lake Michigan by the Sanitary District of Chicago, U.S. House of Representatives' Document No. 6, 59th Congress, 1st session (Washington, 1906). (W. P. A.)
