The water jet from the submarine cave is extremely fast, up to 240km/h, forming a water flow barrier that small marine animals can't pass through. Nowadays, many countries use undercurrent to keep fish in captivity, trap them in an area, and bring seabed microorganisms to the surface to fill their stomachs, which saves money and time.
Some marine animals that want to migrate long distances use undercurrents to migrate to far places, temporarily escaping from human hunting and reproduction.
Extended data:
In the process of seawater surging, an undercurrent will be formed due to the blocking effect of submarine reef on seawater backflow, which is different from the surface water flow direction. Under the action of radiation stress and pressure difference of sea waves, after the waves are broken, the high water bodies piled up on the shore pass through the broken waves and flow into the zonal surface current of the sea.
The velocity is mostly 0.3- 1 m/s, the fastest is 3 m/s, its length is 30- 100 m or even longer, and its flow direction is almost perpendicular to the coastline, which can quickly drag strong swimmers into the deep water and become a dangerous "killer" of coastal leisure tourism.
Baidu encyclopedia-seawater undercurrent