This article is written by Geoff Peach, of The Lake Huron Centre for Coastal Conservation. It first appeared in the Centre’s August 2012 e-newsletter, released this week. The Goderich-based non-profit charity advocates wise stewardship of Lake Huron’s coastal ecosystems. To learn more about the Centre and sign up for its e-newsletter, please visit online.
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Last week my daughter called me on her cell phone from our Lake Huron cottage. She was standing on the beach, seeing the lake level drop dramatically before her eyes. She asked me, with a sense of alarm, “What’s happening to my lake?!” She described that the shoreline had suddenly moved out about five metres from its former position, exposing rocks and lakebed. I told her that she was in luck, as she was witnessing a lake phenomenon known as a seiche (pron. Saysh).
The Great Lakes can form seiches—oscillations of surface water that can change water levels by a metre in just moments The term “seiche” apparently originated from the Latin word siccus which means dry or exposed (referring to the exposure of the lake bed). They form when wind and air pressure change and cause the surface of a lake to rock back and forth. While small-scale seiches go unnoticed, large seiches are powerful enough to bang anchored ships together. This happened in Goderich harbour several years ago, causing some significant damage to moored ships. Seiches can also impact the biology of lakes by pulling nutrients and other sediments into the upper layers of the lakes.
A seiche has to occur in an enclosed body of water such as a lake, bay or gulf. A seiche is a standing wave that oscillates in a lake as a result of seismic or atmospheric disturbances creating huge fluctuations of water levels in just moments. The standing waves slosh back and forth between shores of the lake basin, often referred to as tide-like changes of the Great Lakes, by many.
Most seiches on the Great Lakes result from atmospheric disturbances and a cease in wind, not seismic activity or huge tidal forces.
[Standing waves - The waves in a seiche are stationary in the horizontal plane and do not progress forward. The waves move up and down, but not forward like wind waves at sea. That's why these waves are called as standing waves rather than progressive waves.]
Seiches can last from a few minutes to several hours and can be very dramatic.
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 storm systems, having strong barometric 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 metres on both sides of the basin. With each circuit, some energy is lost, and the seiche decreases in height before finally settling down.
The wind can cause seiches on almost any day, but most fluctuations are small less than a few centimetres in height and go unnoticed.
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 2 metres.
A seiche is an interesting thing to observe. As a seasoned beach-goer, my daughter had never experienced a seiche first hand. It was something she won’t soon forget.
2 Comments on "Lake Huron seiche is like water splashing in a tub"
Great information-Thank-you
We believe seiches may contribute to rip current drownings on the Great Lakes. When a seiche runs into a pier or jetty the water flows around it much like a rip current. People may panic and try to fight the current, tire and drown.
According to the Great Lakes Surf Rescue Project there have been 62 fatal drownings on the Great Lakes so far this year, last year there were 87. Rip currents are the biggest danger on the Great Lakes and everyone should learn what to do if they’re caught in one. FLIP, FLOAT and FOLLOW!
FLIP over onto your back and try to keep from panicking, FLOAT with the current to see where it is taking you, DO NOT FIGHT against the current, it’s like a treadmill. FOLLOW the safest path back to safety. There is no such thing as “undertow” the current will not pull you down. Control the panic and go with the flow.
For more information:
http://david-benjamin.blogspot.com/
http://www.facebook.com/pages/Great-Lakes-Surf-Rescue-Project/120501018657