Seiches on the Great Lakes often mistaken for tides
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EmailSeiches can often enhance rip current dangers on the Great Lakes.
Michigan Sea Grant and Michigan State University Extension often receive questions from the public about the existence of tides on the Great Lakes. Many people often mistake a seiche for a tide on the Great Lakes.Tides are changes in water levels as a result of gravitational forces of the moon and the sun that are more pronounced on the largest bodies of water such as the oceans. The U.S. Army Corps of Engineers, the National Oceanic and Atmospheric Administration (NOAA), and the National Ocean Service (NOS) documented that the spring tide, which is the largest tide on the Great Lakes, is less than 2 inches. Thus the minor tidal changes on the Great Lakes are extremely small when compared to the greater fluctuations of seiches caused by changes in wind and atmospheric pressure.
So then what is a seiche? When you observe water sloshing back and forth in a bathtub you witnessed a small-scale seiche. At a larger scale, a seiche occurs in large bodies of water such as the Great Lakes. Seiches result when strong winds and rapid changes in atmospheric pressure push water from one end of the lake to the other. The water rebounds to the other side of the lake when the wind stops. As a result the water then continues to oscillate back and forth for hours or even days. The time period between the "high" and "low" of a seiche can be as much as four to seven hours.
The magnitude of seiches vary depending on the Great Lake. Lake Erie can exhibit large seiches when strong winds blow from southwest to northeast. In 1848, a 22-foot seiche resulted in 78 deaths. In 1929, a seiche flooded the Grand Haven, Mich., pier sweeping people off while strong rip currents carried several more away from the beach resulting in 10 deaths. In 1938, a large seiche occurred in Holland, Mich., that swept people from the pier and away from the beach resulting in 5 deaths.
Strong rip currents are often associated with a seiche because of the very dangerous water fluctuations and movements of abnormal currents. Many of the seiches that have taken lives have occurred on Lake Michigan with a few somewhat large and destructive seiches taking place on lakes Superior, Huron and Erie. A series of seven drownings along the southeast shoreline of Lake Michigan on July 4, 2003, were associated with a moderate to strong seiche of the basin. During this single event, seven rip current-related drownings were reported within a three-hour period along a concentrated three mile section of beach.
To assist in the monitoring of seiches, National Ocean Services maintains a network of over 50 tide gauges around the Great Lakes, which measures the lake levels at 6 minute intervals as well as providing wind data, air temperature, relative humidity, and barometric pressure.
Michigan Sea Grant helps to foster economic growth and protect Michigan’s coastal, Great Lakes resources through education, research and outreach. A collaborative effort of the University of Michigan and Michigan State University, Michigan Sea Grant is part of the NOAA-National Sea Grant network of 33 university-based programs.
