WORDS on WEATHER & CLIMATE

Could a tsunami occur in Lake Michigan?

by CRAIG JAMES

After a large tsunami somewhere in the world, it has been very common to hear the question, “Can a tsunami occur in Lake

Meteorologist Craig James, new Squire columnist

Michigan?” Fortunately, the answer to that is, “If you mean something like what just happened in Japan, NO.” We have no seismic faults in our area to cause large earthquakes that can generate what we saw in Indonesia in 2004 and Japan last week. In case you haven’t heard, according to the United States Geologic Survey, the earthquake moved the island of Japan eight feet and shifted the axis of the Earth several inches. Now that is power!

Tsunamis used to be called tidal waves, but they have nothing to do with the tides. They propagate through the open ocean at speeds over 600 mph. There is little evidence of the wave out over the deep open water, but as the wave approaches the shore and the water gets shallower, the wave slows down and can build to immense heights.

However, we do get an event in Lake Michigan, and in any large lake actually, called a seiche. It is pronounced “ saysh” and is a French word meaning to sway back and forth. It is defined as a temporary disturbance or oscillation in the water level of a lake or partially enclosed body of water, especially one caused by changes in atmospheric pressure. Thunderstorms frequently produce strong downdrafts of cold air that increase the barometric pressure along the leading edge of the storm. The wind plus the higher pressure can push water away from one shoreline of a lake toward the opposite shore.

This is especially pronounced on Lake Michigan with a storm moving along the long axis of the lake. It is less frequent with a west-to-east moving storm but does occasionally happen. A seiche moves much more slowly than a tsunami, usually about the speed of the thunderstorm winds, but once the swell of water moves onshore, the water quickly retreats back into the lake, generating deadly rip currents. The water can then slosh back and forth for hours until lake levels return to normal.

Large seiches on Lake Michigan are rare, but according to a Michigan State University Geography Department website about seiches, on July 4, 1929, while 45,000 people were gathered at Grand Haven State Park to celebrate the holiday, a series of seiches hit the shoreline after an early morning storm. The seiche completely buried the Grand Haven pier, sweeping people off into the water, while strong rip currents from the retreating water carried several more away from the beach, resulting in 10 fatalities.

Other very deadly seiches occurred at Holland State Park in 1938 and in Chicago in 1954, where the water rose as much as 10 feet in a few minutes. On July 2, 1956, in Ludington, the lake was described as calm before the water level suddenly rose 10 feet and pushed inland over 150 feet. After the first surge of water, the lake receded 15 feet below the normal water line only to return again another 15 minutes later.

Compared to other localities, Michigan is one of the safest places in the world from natural disasters such as large earthquakes and tsunamis, but it is not unheard of for a distant earthquake to cause a small seiche in the Great Lakes. Believe it or not, swimming pools are especially prone to seiches caused by earthquakes, as the ground tremors often match the resonant frequencies of small bodies of water. It is reported that the massive earthquake in 1964 in Alaska, caused small seiches in swimming pools as far away as Puerto Rico.

However, unlike devastating tsunamis, seiches rarely cause much damage in the Great Lakes, and most go unnoticed since they are relatively subtle and imperceptible, causing water levels on beaches to rise just a foot or less. But do pay attention to any rip current warnings issued by the National Weather Service. Rip currents are often generated by seiches caused by thunderstorms and claim several lives each year on the Great Lakes.

 

Craig James has been retired since July 1, 2008,

after 40 years of broadcasting television weather. He was chief meteorologist at WZZM-TV for 12 years and

chief meteorologist at WOOD-TV for 24 years. He is

a graduate of Penn State University, where he received

a Centennial Fellowship Award. He was also honored as a Fellow of the American Meteorological Society.

 

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