If you have been to the seaside, you must have seen the phenomenon of rising and falling tides in the sea: at high tide, the water in the ocean will surge to the shore, inundating the beaches and reefs along the coast; at low tide, the sea will quietly recede, removing the original submerged areas exposed. In this way, the sea rises and falls periodically, usually twice a day. During the day, we call the rise and fall of the sea water "tide" and at night, we call it "Xi". The area that is submerged at high tide and exposed at low tide is called the "intertidal zone". You must find it strange. Since the sea water rises significantly during high tide and can submerge the normally exposed areas, where did the water go after low tide? Did it disappear into thin air?
To understand this problem, we must first understand why the water fluctuates. Newton's "law of universal gravitation" tells us that there is gravity between celestial bodies, and the rise and fall of sea water is caused by the tide-generating force generated by the moon and the sun. Under the action of celestial tide-generating forces, the global sea surface will form an ellipsoid with its major axis pointing to the celestial body. Due to the rotation of the earth, the sea surface height of a certain place on the earth changes with different positions on the ellipsoid, forming a undulating wave state and forming a tidal phenomenon. In shallow sea areas, due to the influence of shoreline and water depth, the tides show complex fluctuations. For a location, the peaks correspond to high tides, and the troughs correspond to low tides. Due to the difference in pressure between the trough and the peak, the water flows from the peak area to the trough area. With the constant changes of high tide and low tide, water flows back and forth in the trough and peak areas. Therefore, at low tide, water only temporarily flows to nearby low tide areas, but flows back at high tide.