CHAMPAIGN, Ill. - Spring and summer storms that create thunder and lightning on land also cause tsunami-like waves on the Great Lakes, bringing water surges onshore and jeopardizing docked boats and beach lovers, according to David Kristovich, head of the Climate and Atmospheric Science section with the Illinois State Water Survey, Prairie Research Institute at the University of Illinois.
Waves that behave much like tsunamis, or meteotsunamis because they are caused by weather, are a phenomenon in which the water level rises in lakes over minutes to a couple hours. The water level rises of meteotsunamis occur quicker than those of the more well-known seiche, which is when water in the lakes slosh back and forth over a period of many hours. Meteotsunamis have been responsible for water level rises by as much as 18 feet. Typically though, meteotsunamis raise the water level 1 to 3 feet.
University of Illinois researchers, working with scientists from the University of Wisconsin at Madison, studied meteotsunamis and the weather causing them throughout the Great Lakes using 20 years of data, discovering that a particular type of storm–large thunderstorm systems in spring and summer–usually provide the energy to drive these events. The Great Lakes in general have about 80 such meteotsunami events causing lake rises of at least 1 foot each year.
The water level observing site in Calumet Harbor in Illinois experiences the most frequent and largest meteotsunamis of anywhere in the Great Lakes, possibly because of the typical motions of thunderstorm systems generating them. Dr. Adam Bechle and Prof. Chin Wu (at Wisconsin) found that local features, such as the bowl shape of southern Lake Michigan, also play critical roles in meteotsunami size and frequency.
Different storms respond differently when they reach the water. Nearly all storms weaken over lakes, but some weaken slowly, while others weaken suddenly. In the Great Lakes region, thunderstorms cause meteotsunami through rapid local variations of atmospheric pressure and the strong winds that start the up/down motions of the water surface. For these waves to continue and grow across the lake, it is thought that the storms need to move with them. What’s surprising is when meteotsunami occur.
“The time periods when meteotsunamis occur most often is one to two months earlier than when thunderstorms are most frequent,” Kristovich said. “We don’t fully understand why the peak times are different.”
The study of meteotsunamis is important because they can be dangerous. Dr. Bechle and Professor Wu found that deaths have occurred as a result of the large meteotsunamis. For example, on July 4, 1929, a 20-foot wave surged over the pier in Grand Haven, MI, killing 10 people.
Various monitoring sites measure and predict short-term and long-term waves; but so far, there is no system in place for predicting meteotsunamis.
“The first step is understanding how certain types of storms interact with the cooler summertime lakes to cause meteotsunamis, and the second step is predicting when conditions are right for these interactions,” Kristovich said.
