Seishi — standing waves in lakes and seas

Seishi <TAG1> are special waves that occur in confined or semi-enclosed bodies of water when water begins to oscillate back and forth like a pendulum. Unlike normal waves moving on the surface, seishi stand still: the water level rises at one end of the lake, and at the other at this time it drops. The process is then repeated in the reverse direction. Such fluctuations can be observed in lakes, bays, fjords and even in large reservoirs.

The cause of seishas is usually long strong winds or a sharp change in atmospheric pressure, which shift the water to one shore. When the wind subsides or the pressure equalizes, the water «rolls back and begins to fluctuate until equilibrium is established. Seishi can also form after earthquakes —, then they are called seismic. In such cases, the water in the lakes can fluctuate for minutes or even hours after the tremors.

In addition to superficial ones, there are internal seishi. They are not formed on the surface, but inside the reservoir, between layers of water of different temperatures or densities. These internal fluctuations can be significantly greater than seen externally and strongly affect the ecological processes of — water mixing, oxygen and nutrient distribution.

Next to the concept of seish is often mentioned water boron <TAG1> is a completely different phenomenon. Water boron is observed in narrow river mouths when, at high tide, seawater breaks in against the current, forming a high and moving wave that rolls up the river. So if boron — is a moving tidal wave, seisha — is standing. It does not move forward, but only oscillates within the reservoir.

One of the most famous places where seishi have been observed is Scottish loch Ness. Scientists have confirmed that it regularly contains internal seishi —, large underwater waves that move along the lake along the border between cold and warm layers of water. Such underwater vibrations can reach tens of meters in amplitude, although the surface of the lake remains almost calm. It was these natural phenomena, according to scientists, that could explain «strange waves» or unexpected movements of water, which were sometimes mistaken for manifestations of a mythical monster.

Seishi — is not only an interesting natural phenomenon, but also an important factor for hydrology. They affect water mixing, temperature and oxygen distribution, and in harbors they can create strong level fluctuations that are dangerous for ships and berths. Modern scientists monitor seishi using water level sensors, buoys and temperature probes to better understand how they affect ecosystems and the behavior of water bodies.