The water of the oceans is in constant motion. The gravitational pull of the sun and moon oscillates the surface of the oceans twice a day while the wind agitates it into waves.
The surface of the sea exerts a frictional drag on the bottom layer of a wind blowing over it, and this layer exerts a frictional drag on the layer above it, and so on. The top layer has the keast frictional drag exerted on it which means that the layers of air move forward at different speeds. The air tumbles forward and finally develops a circular motion. This motion causes a downward pressure (DP) on the surface at its front, and an upward pressure (UP) at its rear, and this causes the surface to take on the form of a wave.
The back of the wave tumbles forward but it moves back later and slows the forward movement at the front of the wave. The wave now grows bigger.

The highest point of a wave is the crest and the lowest point is the through. The difference between the two is known as the wave height.
The height of a wave increases if the wind blows strongly for several hours, and waves of considerable height develop in open oceans if a strong wind blows for several days. The size of a wave depends upon the strength of the wind. The duration of the wind and the fetch (the distance of open water over which the wind blows). The stronger the wind, the longer it blows and the greater the fetch, the more powerful the wave. Storm waves are particularly powerful. The limiting factor in all wave development is the length of the fetch. Seas such as the Irish, Baltic and North Sea hate short lengths of fetch and the waves of these seas are never as large as those of open oceans. Very powerful waves move in from the long fetch of the Atlantic and operate along the coasts of south-west England and Ireland. The height of these waves is further incrased by the prevailing westerly winds whose direction coincides with the direction of fetch.

Winds generate waves and each wave has a circular movement. When a wind is very strong the wave steepens, i.e. its height increases but the wave length remains the same. When a wind abates the height decreases and the wave length increases. The same thing happens when steep waves enter calmer more water. As the height decreases the wave becomes more undulating and regular in size and direction. This type of wave movement is called a swell. When a wave enters shallow water, frictional drag on the bottom of the wave causes the top of the wave to move forward, i.e. the wave breaks.

Wind generated wanes are called sea waves. They are usually made up of a number of waves of different lengths superimposed on one another. As we have seen these waves become more regular as they move into calmer water. Swell waves are straight and long, and they travel great distances across the oceans maintaining most of their power.

When a wave enters water whose depth is less than the length of the wave, its velocity decreases. This causes the wave length to decrease which in turn results in an increase in the height of eventually breaks. The water thrown up the beach as the swash and that which drains down the beach under gravity is the backwash.

The circular movement of water in a wave. Notice how the water moves forward on the crest and backward in the trough. When a wave moves towards the shore the circular form becomes elliptical. When waves of long wave length and low height approach a gently sloping beach, the ellipse becomes horizontal. When the waves break, the swash sweeps up the beach as a sheet of water often reaching the upper beach. Most of the swash soaks into the beach which means that there is very little backwash. Waves of this type are called constructive or spilling waves.

High waves of short wave length have an allipse which is vertical. When these waves break on a steeply sloping beach, the water plunges forward into the trough. The steepness of the slope prevents a good development of swash but the backwash is very powerful. It is this that carries material down the beach. Waves of this type are called destructive or plunging waves. It should be noted that small waves breaking on a steeply sloping beach tend to spill rather than plunge.

Waves travel in shallowing water in the offshore zone as they approach the shore. We have already seen that frictional drag by the sea bed retards the bottom of a wave. Usually the sea bed in the offshore zone is not uniform, i.e. the depth of the water varies from one place to another. This results in the waves in the shallower water being retarded mote than those in the deeper water. This causes the wave crest to become curved. This is known as wave refraction. Along a shore which consists of headlands and bays, the configuration of the coast. This results in wave energy being concentrated around the headlands and being spread out in the bays. This explains why headlands have cliffs while bays have beaches at their heads.

The action of waves
The interaction between a wave and the beach largely determines whether a wave eodes or deposits. Usually steep waves are constructive, i.e. they deposit. The wave period, which is the time taken by successive wave crests to pass a given point, directly influences the nature of the backwash. For example, if a wave breaks onto the backwash of a preceding wave, then the swash has only limited action while the backwash becomes dominant and effects erosion, but if the wave breaks after the backwash of the preceeding wave has died down, then the swash reaches well up the beach and deposition by the swash becomes dominant. It should also be noted that an onshre wind helps waves to erode.

The wasteful waves
The oceanic storms are coused by meteorological causes for example the wind’s power, which twists to the coast the water from the great surface of the sea. The waves were come into existence in the oceanic storms, destroy the protective dams of the coasts. The oceanic flood’s other, specially warning kind – frequently at the Pacific ocean – the oceanic seism in Japanese, called cúnami. It is the sudden motion of the depth of the ocean, an oceanic wave coused by earthquake or vulcanic broken. The hiding of waves coused by the cúnami with about 800 kilometres/hours speed run over the ocean. In the middle of the sea it couldn’t be noticed but if it approaches to the coast, where the sea is more depthless, it’s behaviour suddenly changes: it’s speed and the waves length decrease, but the tallness grately grow.Arriving to the coast the water of the sea firstly with unnatural speed moves back, but sooner it comes back to the coast with horrible wave hitting, and falls into the gulves, distroyes the settlements; and the ships are twisted hundred and hundred metres into the land’s core. Nowadays National Warning Equipment is being operated, which is predicts the date of the cúnami’s arriving in Pacific ocean’s territory.

The gratest wave in the world was come into exsistence by the cúnami, that scourged Japan on the 24th of April in 1771: it was 85 metres tall! An other that was measured on the 28th of March in 1964, was 67 metres tall.

 

This picture shows the flat in the Ganges & the Brahmaputra’s delta. It was flooded in 1988, September. In the foreground the huts and the rice lands are hardly seem in the water. Similar to the flood on the 7th of October in 1937, which caused 300 thousand people’s death, the flood at the beginning of September, in 1988, was caused by a cyclon at the Bengal Bay’s territory and it caused oceanic storm, that raised the surface of the sea 4-5 metres than to the average was.

Made by: Anita