Waves caused by the local winds differ greatly in size and other characteristics. However, they are all high relative to their lengths. The orbital velocity of water particles is great. But the rate of advance of such waves is low, because it is proportional to the length of the wave which is not very long.
The plunge of such waves is almost vertical; so much energy is lost in the process. Besides, still more energy is consumed by the eddies or rollers as they advance up the beach. Although the send is weak, even then it transports a considerable volume of water up the beach. The same water returns as a relatively powerful backwash.
As this meets the oncoming send, it reduces its effect. As a result of this, these sea waves tend to drag materials down the beach towards the open ocean. These waves, therefore, are called destructive waves.
Destructive waves fall into two distinct categories; seismic waves and storm waves.
Tsunamis are called seismic waves as they are produced by the submarine earthquakes. They are often called tidal waves, but the fact is that they are hardly related to tides.
The wavelength of the tsunamis may be as long as 160 kilometers, and such waves travel at a very high velocity, sometimes reaching 650 kilometers or more per hour.
However, in the open sea their heights hardly exceed 1 meter, but when they travel in shallow coastal waters, they may develop into waves having abnormal heights causing unimaginable destruction in a very short period of time.
Landslide surges are the highest waves ever formed. They develop into more or less restricted water bodies, when a massive rock falls into the water. Such destructive waves are reported to have occurred in Lituya Bay, Alaska, when a mass of rock, about 40 million cubic yards fell from a height of about 1000 meters into this bay causing a surge of water on to the opposite shores of the bay to a height of about 570 meters.
This surge produced a gravity wave which moved out of this bay at a velocity of about 160 kilometers an hour. Similar destructive waves include avalanche waves and iceberg waves. These destructive waves, upon reaching the coast, form very powerful and destructive breakers, even when the sea surface is calm and glassy.
Storm waves caused by hurricanes and other local storms prove very disastrous. The waves of extraordinary heights produced by these storms play havoc, particularly in the low-lying coastal areas. Actually they involve huge loss of life and property in the coastal zone. Describes the state of the sea at varying wind speeds.