March 17, 2011 // 0 Comments

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 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 […]