Erie, Lake

Lake erie is the fourth largest of the five Great Lakes and the 12th largest freshwater lake in the world. The history of Lake Erie is complex. Approximately 2 million years ago, a basin, or lowland, in the present-day Erie basin served as the valley of a once east-flowing Erigan River. This drainage system was destroyed by the first of several major glacial advances that deepened and enlarged the basin. The problem for geologists was that each successive glacier destroyed the evidence of the preceding one, making a complete and thorough history virtually impossible.

A more detailed history of Lake Erie can be traced as far back as the retreat of the Wisconsinan—the last Pleistocene glacier—some 14,500 years ago. Scientists using radiocarbon-dated sentiments, detrital transport, hardwater, inorganic carbon contamination, postdepositional compaction, and other sampling procedures have added considerably to our understanding of Lake Erie's evolution.

In its present form, Lake Erie is relatively young according to geologists, with a lifespan of less than 4,000 years. Lake Erie has an elevation of 571 feet (174 meters) above sea level, a surface area of 9,940 square miles (25,745 square kilometers), a length of 241 miles (388 kilometers), and a breadth of 57 miles (92 kilometers) at its widest point. Its maximum depth is 210 feet (64 meters), its water volume is 116 square miles (484 square kilometers), and its residence time—the time lake water takes to renew itself—is 2.6 years. Its primary source is the Detroit River and primary outflow is the Niagara River into Lake Ontario.

Lake Erie has a number of interesting characteristics. Its basin is comprised of Devonian shale in the east and limestone and dolomite (Silurian and Devonian carbonates) in the west, which are more resistant to erosion. Hence, the lake is shallow in the west (averaging less than 25 feet) and much deeper in the east (reaching 210 feet) where glacial ice was able to remove the limestone. The basin is also shallow at its most southerly points (where it averages less than 25 feet) because that is where the glacial ice was thinnest pending its retreat. When glaciers flow over resistant bedrock, they leave scratches in the surface known as striations, which are produced by grinding stones caught between the ice and the bedrock. Striations of up to three feet are found commonly in Bass Island's hard Silurian limestone in western Lake Erie. Waves in shallow water also tend to be steeper than those in deep water, and thus Lake Erie is known for choppy waters during storms.

Lake Erie's ecology and hydrology also have some unique features. Because Lake Erie (like the other Great Lakes) is relatively young, its water contains relatively few species of fish. The food chains are short, relatively simple, and easily disrupted, such as when spectacular changes in lake levels result from tilting or imbalance of the lake surface produced by winds and changing barometric pressures. Consequently, Lake Erie has risen for hours or days over an appreciable area by as much as 8.4 feet. The lake also has small tides called seiches, which can be measured in inches rather than feet, that can last for days. Another unique feature of the Great Lakes including Lake Erie are seasonal thermoclines (often called thermal bars), which are horizontal interfaces that separate the warmer water at the surface, or epilimnion, from the colder deeper water, or hypolimnion. These thermoclines form during the spring and break up during the fall.

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