What is a Seiche?

A seiche is an oscillating standing wave in a body of water. The term seiche pronounced saysh) can be understood by the sloshing of water back and forth in a swimming pool. The same phenomenon happens on a much larger scale in vast bodies of water including bays and lakes. A seizure can happen in any enclosed or semi-enclosed body of water.

Causes of Seiche

Powerful winds and rapid changes in air pressure shift water from one end of a body of water to the other, causing seiches. The water rebounds to the other side of the enclosed area when the wind stops blowing. For hours or even days, the water begins to oscillate back and forth. Seismograms may also be caused by earthquakes, tsunamis, or extreme storm fronts along ocean shelves and harbors.

Seizures are also considered to be caused by earthquakes. During major earthquakes, swimming pools often experience particularly dramatic seiches. As the length of a seismic wave (the interval between two waves) interacts with the timescale of waves sloshing in a tub, the effect can be amplified.

Coastal Seiches

Coastal seiches, which occur in harbors or open coastal waters, usually last minutes to hours, with heights varying from centimeters to more than one meter in extreme cases. Seiches may be triggered directly by meteorological, geological, or other processes that disturb a coastal water body, as well as indirectly by open sea processes operating through the coastal shelf or harbor mouth. Long open sea waves, such as tsunamis, tsunami-like meteorologically produced long waves, and tide-generated internal waves can cause large and dangerous coastal earthquakes.

Lake Erie and Seiches

Seiches are common in Lake Erie, mostly when winds flow from southwest to the northeast. In 1844 a huge seiche ( 22 foot) broke a 14 feet high sea wall. This incident killed 78 people and also dammed the ice to a point that Niagara Falls stopped flowing for a time. Strong winds caused waves 12 to 16 feet high in Lake Erie in 2008, causing flooding near Buffalo, New York. During the summer, after the passing of afternoon squall lines, Lake Pontchartrain, Louisiana, is known to shape tiny seiches.

Great Lakes and Seiches

The interval between the "up" and "low" of a seiche can be as long as four to seven hours in some of the Great Lakes and other large bodies of water. This is often mistaken for a tide because it is somewhat close to the interval between high and low tide in the oceans.

The water levels of the Great Lakes are a hot topic for many people. Seasonal, long-term, and short-term water level fluctuation are all common occurrences in the Great Lakes. Seasonal variations are measured over a year and are made up of the four seasons that change. Long-term levels occur over a long period, typically a few to several years. The amount of water in the Great Lakes via the hydrologic cycle is usually seen through seasonal and long-term shifts. Seasonal and long-term variations in lake levels are frequently discussed by boaters, fishermen, marina owners, and others who are connected to the Great Lakes in some way. Short-term fluctuations, which can last anywhere from minutes to hours to days, are seldom discussed (Gauthier and Manninen, 1999; US Army Corps of Engineers and Great Lakes Commission, 1999).

Wind set-up or storm surge, like seiche, are examples of short-term variations that often occur on the Great Lakes. A storm surge, also known as a wind set-up, occurs when high sustained winds from one direction force the water level up at one end of the lake while dropping it by the same amount at the opposite end.

Differences between Tsunami and Seiche

A tsunami is a large-scale seafloor movement that occurs as a result of a large earthquake, huge submarine slide, or exploding volcanic island.

A seiche is a collection of standing waves triggered by earthquakes or landslides in a totally or partially enclosed body of water. Harbors, bays, lakes, rivers, and canals may all be affected by Seiche’s action.

Although tsunamis and earthquakes are uncommon in Puget Sound, it's important to be aware of the dangers they can pose. A sudden or unforeseen water recession is one of the early warning signs of a tsunami. Additional waves will arrive a few minutes or even hours later after the first one. Waves grow in size over time, and coastal flooding may sometimes occur before the largest wave.

Recent studies on the chances of a large earthquake off the coasts of Washington, Oregon, and Northern California has reported that within sometime after a major quake, the nearby households could be affected by local tsunami waves.

Tsunamis and seiches are also a possibility, according to local studies of an earthquake on the Seattle Fault.

Differences between Seiches and Meteotsunamis

While seiches and meteotsunamis are often lumped together, they are two distinct events. Winds and atmospheric pressure may also contribute to the formation of seiches and meteotsunamis; however, winds are usually more critical in the formation of seiches, while pressure is also a significant factor in meteotsunami formation.

A seizure and a meteotsunami may often happen at the same time. Seiches are standing waves with longer periods of water-level oscillations (typically three or more hours), while meteotsunamis are progressive waves with wave periods restricted to the tsunami frequency band (two minutes to two hours). Seiches are normally restricted to basins that are partially or completely sealed, such as Lake Erie. Tsunamis can happen in these basins, but they also happen on the open coast. A single meteotsunami can travel great distances and affect a vast area of coastline.

Context and Applications   

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for 

• Bachelors in Science Physics
• Masters in Science Physics