Tuesday, January 27, 2015
Strange Oscillations: Mysterious ‘seiche‘ Drops Bay Water Level by 18 Inches in Two Hours
On Tuesday morning, June 4th, 2002, West Grand Traverse Bay‘s water level dropped an astonishing 18 inches in less than two hours. A sailor was getting his boat ready for summer mooring and by the time he was all set to go - too late! His boat was stuck in a sandbar due to the sudden water level drop.
Known as a seiche, it is a phenomenon which occurs frequently on the bays of Northern Michigan. What is a seiche? Pronounced “saysh,“ you may compare it to water sloshing in a bathtub. Seiches are tide-like rises and drops in coastal water levels, (occurring both in fresh water and ocean waters) caused by prolonged strong winds that push water toward one side of the water body. This causes the water level to rise on the downwind side of the lake and to drop on the upwind side. As the wind diminishes, the water sloshes back and forth, with the near-shore water level rising and falling in decreasingly small amounts on both sides of the lake until it reaches equilibrium.
Seiches occur most in waters that are more or less surrounded by land, such as lakes, fjords and gulfs. Otherwise there would not be that sloshing back and forth that characterizes a seiche. Water blown onto a shore will just ebb back into the ocean if there is no opposite shore to reflect the wave. Seiches can also be caused by earthquakes, even very distant ones. Seiches triggered by earthquakes thousands of miles away have been reported.