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October 26, 2011—The arrival of fall is a good time to consider one of the interesting effects storms can have on Lake Erie. Imagine pointing the blast of a high-powered leaf blower onto a long tub of water. Water would slosh up against the far end of the tub, dropping the water level at one end while pushing it higher at the other. When you turn off the leaf blower, the water would attempt to return to equilibrium, sloshing several times from one end of the tub to the other.
This is exactly what happens to Lake Erie when a seiche (pronounced “saysh”) occurs. A seiche is a phenomenon whereby winds on the lake cause the water level to rise at one end and drop at the other. This rise in water level is sometimes called a wind tide, wind set-up, or storm surge.
Lake Erie is especially subject to this phenomenon during certain conditions. The lake’s long axis is oriented southwest to northeast. Strong sustained winds that coincide with this orientation push water away from the southwest end of the lake, towards Buffalo, if they blow from the southwest. If they blow from the northeast, water is pushed away from the northeast end, towards Toledo. The lake’s narrow dimensions (in relation to its length) ensure that the wave of rising water, rather than spreading evenly, is directed along the lake’s long axis, until it reaches the opposite end.
The magnitude of a seiche depends on how long the winds blow and is measured in the difference between water levels at Toledo and Buffalo. Most seiches are of small magnitude—maybe 1 to 2 feet—and pass without notice on a roughly daily cycle. But strong winds sustained over many hours can cause the water level between Toledo and Buffalo to differ by up to 16 feet. Storm waves in conjunction with the surge can cause catastrophic flooding at the end of the lake where the water rises and other problems where the water level drops. In Lake Erie’s shallow western basin, a seiche can drop the water level nearly 8 feet, exposing the lake bottom for hours at a time. Docked boats can be damaged as the water drops and the boats settle into soft mud, where they remain stuck after the water returns. Sometimes it appears possible to walk from one island to another.
When storm winds subside, water levels try to return to equilibrium, leading to the most interesting aspect of a seiche—the “sloshing” effect as the surge at one end of the lake rolls to the other end. Soon, the end that previously had the highest water now has the lowest and vice versa. It typically takes from 6 to 12 hours for the wave to travel from one end of the lake to the other, and the back-and-forth rolling usually continues for more than a day. Each time the wave rolls across the lake, it becomes attenuated; so assuming the wind doesn’t pick up strength again, the effect is never as intense at the initial wind set-up. Eventually, to the eye, the wave is indistinguishable from the many small waves that stir the lake surface.
The graph below traces a recent Lake Erie seiche. From October 17 to 21, 2011, the wind shifted widely, from out of the west to out of the northeast, and to eventually out of the west again. The lines on the graph show the response of the water levels at Buffalo (red) and Toledo (blue) to these shifts. The greatest difference in water level was about 7 feet, and as the up-and-down swings of the lines show, the lake never settled to an equilibrium state over these several days.
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Graph illustrating Lake Erie seiche event in October 2011. Click image to enlarge.
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Lake Erie is by no means the only place in the world where this occurs. Any enclosed body of water, such as a bay or harbor, can be affected, and other forces besides winds—earthquakes, for example—can change water levels suddenly. Lake Michigan is known for rare but violent seiches that have swept unsuspecting persons off piers in downtown Chicago.
Further Information
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