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      Seiche!: July 22, 2014

      The seiche at the high point.

      A significant seiche was reported in Munising Bay this past Tuesday morning.

      A seiche is a Great Lakesâ?? â??Tidal Waveâ?? a phenomenon most famous on the largest bodies of fresh water in the world. A seiche is the rhythmic oscillation of a body of water. Seiches on the Great Lakes occur, often in conjunction with severe weather, when prolonged strong winds push water toward one side of the lake causing water levels to rise on the downwind side of the lake and to drop on the windward side. When the wind stops, the water sloshes back and forth. The process can be likened to water sloshing back and forth in a pan after the pan is disturbed.

      The Tuesday seiche was caused by a strong area of thunderstorms that formed mainly over Lake Superior in the morning. The water began rising and falling in Munising Bay reaching a high tideâ??about three feetâ??during the mid to late morning. The water in the bay then rose and fell at regular intervals with decreasing amplitude into the afternoon. Docks were flooded and there was a report of a damaged dock on the east side of the bay.

      The phenomenon probably occurs multiple times during the summer, though the rise and fall is barely noticeable. Every so often, the conditions line up just right for a memorable event. The last time there was a seiche of this magnitude was Memorial Day 2012. There was also a significant seiche reported on the east end of Lake Superior back in the summer of 2006.

      Probably the greatest seiche of modern times occurred on June 19, 1939. A major complex of thunderstorms raked the U.P. from west to east during that morning bringing large hail, damaging winds and deadly lightning. The freakish surge â??unprecedented in the memory of marine menâ?? rose and fell up to five feet over a period of several hours. Docks, fish houses and small boats in Marquette harbor sustained extensive damage.

      Farther up the shoreline to the west, the highway between Lâ??Anse and Baraga was closed; surging water brought debris from the lake over the roadway. On the north shore of Lake Superior, Canadian officials reported a rise of eight feet in 20 minutes in the waters of Heron Bay. It took until the next morning before the lake there reached normal levels.

      What may be the most deadly Great Lake seiche occurred in Chicago on Sunday June 26, 1954. Without warning on that hot summer day a 10-foot wall of water swept seven people to their deaths.