The enormous body of water that forms the seas and oceans of the Earth is subject to movements of diverse nature, similar to what happens in the atmosphere. Water has less density than air, but more than land.
These movements can be summarized in three groups: waves and tides, which are perceived on the surface, and sea currents, which run through the interior and are of great importance in determining the climate.
Vertical displacement: waves and tides
The waves are produced by winds that sweep the surface of the waters. They move the water in a cylinder, without moving it forward, but, when they reach the coast and the cylinder rubs against the bottom, they start a run that ends up unbalancing the body of water, causing the wave to break.
Seismic movements on the seabed sometimes produce gigantic waves called tsunamis.
The tides have a great influence on coastal organisms, which have to adapt to very abrupt changes throughout the intertidal zone: a few hours covered by sea waters and scourged by waves, followed by other hours without water or, even in contact with fresh water, if it rains.
In addition, on some coasts, because of their shape, strong tidal currents are formed, when the waters rise and fall, which drag sand and sediments and remove the funds in which living things live.
In the vicinity of the coast there are usually drift coastal currents, very variable depending on the shape of the coast and the depths of the bottom, which have a lot of interest in the formation of beaches, estuaries and other forms of coastal modeling.
The energy released by the waves in the continuous collision with the coast, the tides and the currents are of great importance because they erode and transport the coastal materials, until they are settled in the most protected areas. In the formation of the different types of coastal ecosystems: marshes, beaches, tidal waves, dunes, etc. the rivers that flow into the place and the nature of the rocks that form the coast also have an important influence
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