When everyone goes to the beach to play, have you ever noticed such a phenomenon: no matter how big the waves are in the distance, when you are close to the coastline, you are always parallel to the coastline. Why?
Before explaining this phenomenon, let's first understand how waves form.
Waves are a wave phenomenon that occurs in the ocean. According to the type, it can be divided into wind waves, surges, tsunamis and so on. The undulating activities of the waves are regular and cyclical. When the waves rush to the shore, the upward and downward movement of the lower water is hindered because the sea water is getting shallower and shallower, and because the object has inertia, the waves of the sea water are stacked on top of each other, more and more, and the wave is higher than the wave. At the same time, as the water depth becomes shallower, the movement of the lower water is subjected to greater and greater resistance, and finally it moves slower than the upper layer, and due to inertia, the highest part of the wave falls forward and lapped on the reef or coast.
When you reach the shore of the shallow water, the water depth is shallow and the wave speed is slower, so the excess energy will push up the waves. As a result, the closer you get to the shore, the higher the waves appear, so sometimes it feels like a sudden surge of waters appears on the shore.
As for why the waves are parallel to the coastline, this is because the first end to approach the coast, due to the early encounter with shallow water, slows down the wave speed, and the far end approaches at a higher speed, and eventually it is almost parallel to the coastline.
When we see waves, we may also think of tsunamis. Unlike the causes of waves, the main cause of tsunamis is the rupture of the seabed crust, which causes the crust to move violently, resulting in huge waves of extremely long wavelengths.
Moreover, the waves generally only fluctuate in a certain depth of the water layer, and the fluctuations of the water body caused by earthquakes are the undulations of the entire water layer from the sea surface to the seabed. It can travel tens of thousands of kilometers at a speed of 600 to 1,000 kilometers per hour on the ocean surface and set off huge waves several meters or even tens of meters high.
If a tsunami forms in the deep sea, the closer it is to the coast, the shallower the water, the smaller the speed of propagation. In the middle of the ocean, where the wave height or the peak of the water wave is less than 1 meter, it is difficult to detect in time. However, during the spread to the coast, the water level difference increases as the water before the tsunami becomes shallower and shallower. The difference in water level caused by this tsunami will flood the beach, flood the coast, and bring great damage.
This article was scientifically checked by Liu Huan, a second-level teacher at Fenglin School in Weihai City, Shandong Province.
Xinhua Network Science Popularization Division
Popular Science China - Scientific principles are one-point
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