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Great Lakes Seiches
Wed Oct 26, 2005
Listen in RealAudio 
Compared to ocean tides, tides in the Great Lakes are pretty small. Yet, other forces can produce significant periodic changes in their water level. One such mechanism is the seiche. Hi, I'm Bryan Yeaton for The Weather Notebook.
Like water splashing in a bathtub, seiches are waves racing back and forth within the lake basin and diminishing with each transit.
Several mechanisms can initiate the Great Lakes seiches. Most often, strong winds blowing along the lake's axis will give the initial kick, but fast-moving squall lines, having strong pressure gradients and downdraft winds, can do the trick, as well. In either case, surface waters are pushed toward the downwind lakeshore.
When the wind dies the accumulated water flows back across the basin, sloshing from one end of the lake to the other. This causes rising and falling water levels of several feet on both sides of the basin. With each circuit, some energy is lost, and the seiche decreases in height before finally washing out.
The wind can cause seiches on almost any day, but most fluctuations are small less than a foot in height and go unnoticed amidst surface wave motions. However, during storm conditions, water-level variances of greater than 16 feet have been measured on opposing lakeshores.
Lake Erie is the most affected of the Great Lakes because it is the shallowest and its basin is often aligned with the forcing winds. The typical seiche on Lake Erie has a period of around 14 hours and water-level range of 6 feet.
Seiches on Lake Michigan have reached ten feet. On June 26, 1954, an 8-foot-high seiche struck Chicago's lakefront. People fishing on the dock in Montrose Harbor, were caught unaware. Eight were killed.
Thanks to our contributing writer, meteorologist Keith Heidorn. Our program is funded by Subaru, and The National Science Foundation.
Today's Links
The Great Lakes
http://t3.preservice.org/T0210274/
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