Waves are formed when wind blows over areas of water; in the case of the sea, the waves may be either constructive or destructive as they break on reaching the land.

There are 2 types of waves-

1. Constructive waves

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Constructive waves have limited energy. Most of this is used by the swash to transport material up the beach.

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Constructive waves are usually:

  • Small in height
  • Gentle in angle
  • Less energy
  • Strong swash and weak backwash

2. Destructive waves

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Destructive waves have much more energy. Most of this is used by the backwash to transport material back down the beach.

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Destructive waves are usually:

  • Large in height
  • steep fall
  • lot of energy
  • Strong backwash

Formation of waves

As you can see in diagram below, water particles within a wave move in a somewhat circular orbital movement, where the energy of water and wave moves towards the shore, and water particles itself stays in its orbit. Water particles or floating objects within circular motion of orbit consist of moving up and down vertically. transfer of energy goes in a horizontal route towards shore.

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When wave reaches shore, velocity of energy will slow down due to the friction of seabed. The circular motion turns more into a elliptical motion where wave eventually breaks upon shore. Note that the top of wave isn't affected by friction, it only becomes higher and steeper until it breaks upon the shore. After this, rest of what used to be wave is the swash, in which it moves forward. Swash moves energy towards the shore, whereas the backwash returns energy down the beach. There is also a term applied for water movement, the fetch. The fetch is The distance wind blows over the surface of the water.

Coastal erosion

waves have the power to erode land, just like rivers. here are four processes:
  • hydraulic pressure: the force of wave in compressing air in tiny holes and cracks in cliffs.
  • Corrosion: this is when weak acids or salts in the seawater dissolve the cliff's rock.
  • Attrition: when movement of waves cause boulders and rocks to collide into each other and to break up into smaller pieces.
  • Abrasion: When large waves heave beach material against cliffs.