Oceanography

Seiches

Standing waves that occur in natural basins are called seiches, and the oscillation of the surface is called seiching. In natural basins, the length dimension usually greatly exceeds the depth. Therefore, a standing wave of one node in such a basin behaves as a reflecting shallow-water wave, with the wave length determined by the length of the basin. In water with distinct layers having sharp density boundaries, standing waves may occur along the fluid boundaries as well as at the air-sea boundary. The oscillation of the internal standing waves is slower than the oscillation of the sea surface.

Standing waves may be triggered by tectonic movements that suddenly hit the basin, causing the water to oscillate at a period defined by the dimensions of the basin. If storm winds create a change in surface level to produce storm surges, the surface may oscillate as a standing wave in the act of returning to its normal level when the wind ceases. The pulsing of a weather disturbance over a lake may also cause periodic water-level change, reaching a meter or more in height. If the period of the disturbing force is a multiple of the natural period of oscillation of the basin, the height of the standing wave is greatly increased.