The National Weather Service is working to determine whether a “meteorological tsunami,” or a “meteotsunami,” occurred on Lake Michigan near Chicago’s Navy Pier early Thursday morning, saying that a water gauge near the site indicated a significant fluctuation in water levels at the location while severe weather pounded the area.
According to a local storm report, a gauge operated by the U.S. Geological Survey indicated that water levels in the lake went up between 18 inches and two feet within a one-hour time frame near the Chicago Lock. A similar fluctuation was reported at Calumet Harbor around the same time, according to officials.
Water level fluctuations are continuing on the lake Thursday, with dangerous swim conditions expected to continue through at least Friday.
Unlike a regular tsunami, which is caused by underground seismic activity, meteotsunamis are driven by rapid drops in barometric pressure, usually caused by fast-moving weather events like severe thunderstorms or squall lines.
During a meteotsunami, a storm generates a wave that moves rapidly toward shore, with the height of the wave being amplified by coastal features as it moves toward the shoreline, according to the National Oceanic and Atmospheric Administration.
According to Michigan Public Radio, meteotsunamis do occur on the Great Lakes, with as many as 100 occurring each year. One such wave struck the city of Chicago in 1954, with a 10-foot meteotsunami striking a pier and killing seven people.
According to Adam Bechle, a researcher cited in the MPR story, even waves that are just a foot tall can sweep people out into the lakes, and the waves can also cause damage to docks, piers and boats.